Unfolded Domain Research Articles

Physical modelling of the nuclear pore complex

Physically interesting behaviour can arise when soft matter is confined to nanoscale dimensions. A highly relevant biological example of such a phenomenon is the Nuclear Pore Complex (NPC) found perforating the nuclear envelope of eukaryotic cells. In the central conduit of the NPC, of ∼30–60 nm diameter, a disordered network of proteins regulates all macromolecular transport between the nucleus and the cytoplasm. In spite of a wealth of experimental data, the selectivity barrier of the NPC has yet to be explained fully. Experimental and theoretical approaches are complicated by the disordered and heterogeneous nature of the NPC conduit. Modelling approaches have focused on the behaviour of the partially unfolded protein domains in the confined geometry of the NPC conduit, and have demonstrated that within the range of parameters thought relevant for the NPC, widely varying behaviour can be observed. In this review, we summarise recent efforts to physically model the NPC barrier and function. We illustrate how attempts to understand NPC barrier function have employed many different modelling techniques, each of which have contributed to our understanding of the NPC.

The Supramolecular Assembly of Intrinsically Disordered Nucleoporin Domains is Tuned by Inter-Chain Interactions

Nuclear pore complexes (NPCs) are the gates that mediate the exchange of all macromolecules between the cytoplasm and the nucleus. They are highly selective: inert proteins bigger than 30 kDa cannot diffuse through NPCs unless they are bound to nuclear transport receptors (NTRs). This selectivity arises from a supramolecular assembly of intrinsically unfolded nucleoporin domains which contain phenylalanine-glycine (FG)-rich repeats, so called FG-repeat domains (FGRDs). Different models for the size and species selectivity of the permeability barrier have been suggested that build on different putative supramolecular assemblies of FGRDs. A controversially discussed question today is whether and how inter-FGRD interactions contribute to the function of the permeability barrier. We have studied the inter-FGRD interactions in monolayers of end-grafted FGRDs which constitute a biomimetic nano-scale model system of the NPC's permeability barrier. A toolbox of biophysical characterization techniques enabled us to relate the strength of inter-FGRD interactions of different FGRD types to monolayer formation and morphology. Our main findings are that inter-FGRD interactions strongly affect the kinetics of formation, the morphology (thickness and lateral homogeneity), and the mechanical properties of FGRD monolayers. Based on these results, we propose that the strength of inter-FGRD interactions in the NPC has evolved to promote the formation of a homogeneous meshwork with a small mesh size. Our results highlight the importance of inter-FGRD interactions for the functionality, and hence contribute important information to refine the model of transport across the nuclear pore permeability barrier.

FRET between a donor and an acceptor covalently bound to human serum albumin in native and non-native states

Fluctuation in the inter-domain distance of a protein, human serum albumin (HSA), in the native, molten globule and denatured states is studied by Förster resonance energy transfer (FRET). For this purpose, a donor (CPM) and an acceptor (Alexa Fluor 488) are covalently attached to HSA. Unfolding of the protein is induced by pH changes as well as by the addition of 6 M GdnHCl and addition of 1.5 M of a room temperature ionic liquid (RTIL, [pmim][Br]). The efficiency of FRET (εFRET) and hence donor (D) - acceptor (A) distances of protein molecules in the native and non-native states are determined using FRET. In the native state (N), there is only one value of εFRET and D-A distance. In the non-native states (molten globule and unfolded) there are multiple values of εFRET and D-A distances. This suggests the presence of multiple conformers in equilibrium in the non-native states. When the protein is unfolded (on addition of GdnHCl or RTIL), separation between the two domains (I and II) increases and as a result εFRET decreases. In the presence of both GdnHCl and RTIL, the protein undergoes compaction (to form N'). However, in spite of the decrease in the overall radius, the D-A distance in the compact state (N') is found to be larger than that in the native state (N) of the protein. In contrast, two acid induced molten globule states of HSA (formed at pH 2 and 4) exhibit high εFRET indicating short D-A distances. In summary, we show that under chemical denaturation HSA undergoes stepwise unfolding and different domains unfold independently.

Hepatitis C Virus NS5B and Host Cyclophilin A Share a Common Binding Site on NS5A

Nonstructural protein 5B (NS5B) is essential for hepatitis C virus (HCV) replication as it carries the viral RNA-dependent RNA polymerase enzymatic activity. HCV replication occurs in a membrane-associated multiprotein complex in which HCV NS5A and host cyclophilin A (CypA) have been shown to be present together with the viral polymerase. We used NMR spectroscopy to perform a per residue level characterization of the molecular interactions between the unfolded domains 2 and 3 of NS5A (NS5A-D2 and NS5A-D3), CypA, and NS5B(Δ21). We show that three regions of NS5A-D2 (residues 250-262 (region A), 274-287 (region B), and 306-333 (region C)) interact with NS5B(Δ21), whereas NS5A-D3 does not. We show that both NS5B(Δ21) and CypA share a common binding site on NS5A that contains residues Pro-306 to Glu-323. No direct molecular interaction has been detected by NMR spectroscopy between HCV NS5B(Δ21) and host CypA. We show that cyclosporine A added to a sample containing NS5B(Δ21), NS5A-D2, and CypA specifically inhibits the interaction between CypA and NS5A-D2 without altering the one between NS5A-D2 and NS5B(Δ21). A high quality heteronuclear NMR spectrum of HCV NS5B(Δ21) has been obtained and was used to characterize the binding site on the polymerase of NS5A-D2. Moreover these data highlight the potential of using NMR of NS5B(Δ21) as a powerful tool to characterize in solution the interactions of the HCV polymerase with all kinds of molecules (proteins, inhibitors, RNA). This work brings new insights into the comprehension of the molecular interplay between NS5B, NS5A, and CypA, three essentials proteins for HCV replication.

Viscoelasticity of Thin Biomolecular Films: A Case Study on Nucleoporin Phenylalanine-Glycine Repeats Grafted to a Histidine-Tag Capturing QCM-D Sensor

Immobilization of proteins onto surfaces is useful for the controlled generation of biomolecular assemblies that can be readily characterized with in situ label-free surface-sensitive techniques. Here we analyze the performance of a quartz crystal microbalance with dissipation monitoring (QCM-D) sensor surface that enables the selective and oriented immobilization of histidine-tagged molecules for morphological and interaction studies. More specifically, we characterize monolayers of natively unfolded nucleoporin domains that are rich in phenylalanine-glycine repeats (FGRDs). An FGRD meshwork is thought to be responsible for the selectivity of macromolecular transport across the nuclear pore complex between the cytosol and the nucleus of living cells. We demonstrate that nucleoporin FGRD films can be formed on His-tag Capturing Sensors with properties comparable to a previously reported immobilization platform based on supported lipid bilayers (SLB). Approaches to extract the film thickness and viscoelastic properties in a time-resolved manner from the QCM-D response are described, with particular emphasis on the practical implementation of viscoelastic modeling and a detailed analysis of the quality and reliability of the fit. By comparing the results with theoretical predictions for the viscoelastic properties of polymer solutions and gels, and experimental data from an atomic force microscopy indentation assay, we demonstrate that detailed analysis can provide novel insight into the morphology and dynamics of FG repeat domain films. The immobilization approach is simple and versatile, and can be easily extended to other His-tagged biomolecules. The data analysis procedure should be useful for the characterization of other ultrathin biomolecular and polymer films.

Biophysical studies with AICD-47 reveal unique binding behavior characteristic of an unfolded domain

APP intracellular C-terminal domain (AICD-47), generated upon γ-secretase cleavage of amyloid precursor’s protein (APP), bears the signature of a classical intrinsically unstructured domain (IUD). Comparing the recent crystal structures of AICD-47 peptides bound to its different adaptors such as protein-tyrosine-binding domain-2 (PTB2) of Fe65 and Src homology 2 (SH2) domain of growth factor receptor binding protein 2 (Grb2), the “conformational switching” of AICD-47 becomes evident. In order to understand different binding processes undertaken by this flexible molecule, upon recognizing different interfaces resulting in different 3D conformations, spectroscopic and calorimetric studies have been done. CD spectroscopy has revealed an overall random coil like structure in different pHs while TFE (2′-2′-2′-trifluoro ethanol) and HFIP (Hexa fluoro isopropanol) induced α-helicity to a certain extent. Binding of Tyr phosphorylated AICD-47 (PAICD-47) to Grb2-SH2 domain was carried out by a favorable enthalpic change (ΔH=−197.5±6.2kcalmole−1 at 25°C) and an unfavorable entropic contribution (ΔS=−631calmol−1deg−1 at 25°C). Alternative conformation of AICD-47 in different biological contexts is another remarkable feature of IUDs which presumably has definitive roles in regulating Alzheimer’s disease phenotype.

Von Willebrand disease biology

*Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden; Department of Thrombosis and Hemostasis, C2-R Einthoven Laboratory for Experimental Vascular Medicine, LeidenUniversity Medical Center, Leiden, The Netherlands; Centre for Haematology, Imperial College London, HammersmithHospital Campus, London;§INSERM U770, Cedex, France; and –Department of Pathology and Molecular Medicine, QueensUniversity, Kingston, ON, Canada

Biophysical characterisation of thermal-induced precipitates of recombinant anthrax protective antigen: Evidence for kinetically trapped unfolding domains in solid-state

Insoluble aggregation or precipitation is one of the most common degradation pathways observed for biotherapeutics; despite this, the structural mechanisms by which this occurs remain poorly understood due to difficulties associated with biophysical characterisation of protein particulates. To address this knowledge gap, we developed a solid-state circular dichroism (CD) technique, which allows in situ measurements of the secondary and tertiary structural changes associated with the formation of visible therapeutic protein aggregates. We demonstrate how solid-state CD, in conjunction with other biophysical and computational methods can aid in gaining valuable insights into the mechanisms and pathways of thermal-induced precipitation of Bacillus anthracis recombinant protective antigen (rPA), the primary immunogen of anthrax subunit vaccine. Using these methods, we show the domains d3 and d4 are the most labile of the four structurally distinct domains of rPA and play the critical role in nucleating the cascade of unfolding and aggregation. During the assembly process, the domains d1 and d2 become kinetically trapped within the insoluble aggregate and reveal previously intractable distinct tertiary structural elements of the rPA native structure. These findings reveal a uniquely detailed insight into the role of rPA domains on protein stability and provide a mechanistic framework for thermal-induced unfolding and precipitation. It also shows that solid-state CD provides a novel approach in characterising protein precipitation that may facilitate rational improvements to the stability of biopharmaceuticals.

Activities of Topoisomerase I in Its Complex with SRSF1

Human DNA topoisomerase I (topo I) catalyzes DNA relaxation and phosphorylates SRSF1. Whereas the structure of topo I complexed with DNA has been resolved, the structure of topo I in the complex with SRSF1 and structural determinants of topo I activities in this complex are not known. The main obstacle to resolving the structure is a contribution of unfolded domains of topo I and SRSF1 in formation of the complex. To overcome this difficulty, we employed a three-step strategy: identifying the interaction regions, modeling the complex, and validating the model with biochemical methods. The binding sites in both topo I and SRSF1 are localized in the structured regions as well as in the unfolded domains. One observes cooperation between the binding sites in topo I but not in SRSF1. Our results indicate two features of the unfolded RS domain of SRSF1 containing phosphorylated residues that are critical for the kinase activity of topo I: its spatial arrangement relative to topo I and the organization of its sequence. The efficiency of phosphorylation of SRSF1 depends on the length and flexibility of the spacer between the two RRM domains that uniquely determine an arrangement of the RS domain relative to topo I. The spacer also influences inhibition of DNA nicking, a prerequisite for DNA relaxation. To be phosphorylated, the RS domain has to include a short sequence recognized by topo I. A lack of this sequence in the mutants of SRSF1 or its spatial inaccessibility in SRSF9 makes them inadequate as topo I/kinase substrates.

Engineering Domain-Swapped Binding Interfaces by Mutually Exclusive Folding

Domain swapping is a mechanism for forming protein dimers and oligomers with high specificity. It is distinct from other forms of oligomerization in that the binding interface is formed by reciprocal exchange of polypeptide segments. Swapping plays a physiological role in protein–protein recognition, and it can also potentially be exploited as a mechanism for controlled self-assembly. Here, we demonstrate that domain-swapped interfaces can be engineered by inserting one protein into a surface loop of another protein. The key to facilitating a domain swap is to destabilize the protein when it is monomeric but not when it is oligomeric. We achieve this condition by employing the “mutually exclusive folding” design to apply conformational stress to the monomeric state. Ubiquitin (Ub) is inserted into one of six surface loops of barnase (Bn). The 38-Å amino-to-carboxy-terminal distance of Ub stresses the Bn monomer, causing it to split at the point of insertion. The 2.2-Å X-ray structure of one insertion variant reveals that strain is relieved by intermolecular folding with an identically unfolded Bn domain, resulting in a domain-swapped polymer. All six constructs oligomerize, suggesting that inserting Ub into each surface loop of Bn results in a similar domain-swapping event. Binding affinity can be tuned by varying the length of the peptide linkers used to join the two proteins, which modulates the extent of stress. Engineered, swapped proteins have the potential to be used to fabricate “smart” biomaterials, or as binding modules from which to assemble heterologous, multi-subunit protein complexes.

On Shaky Ground: The Making of Risk in Bogotá

How does risk become a technique for governing the future of cities and urban life? Using genealogical and ethnographic methods, this paper tracks the emergence of risk management in Bogotá, Colombia, from its initial institutionalization to its ongoing implementation in governmental practice. Its specific focus is the invention of the ‘zone of high risk’ in Bogotá and the everyday work performed by the officials responsible for determining the likelihood of landslide in these areas. It addresses the ongoing formation of techniques of urban planning and governance and the active relationship between urban populations and environments and emerging forms of political authority and technical expertise. Ultimately, it reveals that techniques of risk management are made and remade as experts and nonexperts grapple with the imperative to bring heterogeneous assemblages of people and things into an unfolding technopolitical domain.

Mechanical Stability of the Cardiac Myosin Binding Protein-C (CMybP-C) Motif is Phosphorylation-Dependent

Enhanced cardiac contractility results from phosphorylation within the cMyBP-C motif domain by affecting the interaction of cMyBP-C's N-terminus with actin and/or myosin. We investigated whether motif (i.e. C1C2 linker) phosphorylation alters its structural conformation by characterizing the force-extension behavior of expressed N-terminal cMyBP-C fragments (i.e.C0C3) that contain the motif using atomic force spectroscopy. Proteins were adsorbed onto glass slides, bound non-specifically to SiNi AFM probes, and stretched at 700nm/s. Force-extension traces showed the characteristic sawtooth shape of unfolding immunoglobulin domains, and were well fitted by the wormlike chain model. The model fits produced a median persistence length of 0.36nm and an average C0C3 contour length of 71.5nm, suggesting that the motif is disordered and freely extensible when unphosphorylated. PKA phosphorylation did not change immunoglobulin unfolding force or persistence length but decreased the contour length by 27nm, suggesting that the motif assumed a folded configuration that is stable under load. This was investigated further by varying the extent of phosphorylation using phosphomimetic mutants, in which serines 273, 282, and 302 were replaced with different combinations of alanines or aspartic acids in order to mimic the unphosphorylated and phosphorylated states respectively. While substitution with all alanines or all aspartic acids produced similar results to the control and PKA treated fragments respectively, phosphorylation at only one or two sites did not reduce contour length significantly. This implies that phosphorylation at all three sites is required for motif folding to be stable under load, while partial phosphorylation may result in a fold which is readily extended at low force. In conclusion, cMyBP-C phosphorylation could modulate the cMyBP-C's N-terminal domain interactions with actin and/or myosin by folding the motif in such a way that binding sites for actin and/or myosin are hidden.

Targeted Killing of Escherichia Coli by an Unfolded Protein

The appearance of antibiotic resistant and novel pathogenic strains of E. coli emphasises the continuing need for new antibacterial treatments. Many small proteins exist in nature that kill bacteria by disrupting their membranes but, since human and bacterial lipid bilayers are similar, it is difficult to avoid toxicity to the patient. We study Colicin N (ColN), a ∼ 400 residue globular protein which contains a short unfolded N-terminal domain. The folded region binds to bacteria and kills by forming pores in the inner bacterial membrane. The unfolded N-terminal 90 amino acids (ColN-T) were thought simply to help translocate the toxic domain to the inner-membrane. Here we report the unexpected finding that, in isolation, ColN-T is bactericidal and, although less efficient than ColN, is strictly dependent upon the same receptor proteins, OmpF and TolA. The binding sites for these occupy either end of the linear polypeptide. Also like ColN, ColN-T induces K+ leakage across the inner-membrane. However, unlike most antimicrobial peptides, ColN-T does not disrupt, nor bind to, model lipid bilayers. These data imply that, uniquely, it can induce E. coli killing by OmpF/TolA interactions alone. Since these receptors are only found in E. coli-like bacteria, ColN-T displays the unusual combination of a generic killing mechanism coupled with extreme specificity. As a result, we believe that this unstructured polypeptide antibiotic could point the way to wholly new targets in antibacterial therapy.

Molecular Mechanism of Protein Folding in the Cell

F.-Ulrich Hartl and Arthur Horwich will share this year's Lasker Basic Medical Science Award for the discovery of the cell's protein-folding machinery, exemplified by cage-like structures that convert newly synthesized proteins into their biologically active forms. Their fundamental findings reveal mechanisms that operate in normal physiologic processes and help to explain the problems that arise in diseases of protein folding.

The soluble, periplasmic domain of OmpA folds as an independent unit and displays chaperone activity by reducing the self-association propensity of the unfolded OmpA transmembrane β-barrel

OmpA is one of only a few transmembrane proteins whose folding and stability have been investigated in detail. However, only half of the OmpA mass encodes its transmembrane β-barrel; the remaining sequence is a soluble domain that is localized to the periplasmic side of the outer membrane. To understand how the OmpA periplasmic domain contributes to the stability and folding of the full-length OmpA protein, we cloned, expressed, purified and studied the OmpA periplasmic domain independently of the OmpA transmembrane β-barrel region. Our experiments showed that the OmpA periplasmic domain exists as an independent folding unit with a free energy of folding equal to − 6.2 (± 0.1) kcal mol -1 at 25 °C. Using circular dichroism, we determined that the OmpA periplasmic domain adopts a mixed alpha/beta secondary structure, a conformation that has previously been used to describe the partially folded non-native state of the full-length OmpA. We further discovered that the OmpA periplasmic domain reduces the self-association propensity of the unfolded barrel domain, but only when covalently attached (in cis). In vitro folding experiments showed that self-association competes with β-barrel folding when allowed to occur before the addition of membranes, and the periplasmic domain enhances the folding efficiency of the full-length protein by reducing its self-association. These results identify a novel chaperone function for the periplasmic domain of OmpA that may be relevant for folding in vivo. We have also extensively investigated the properties of the self-association reaction of unfolded OmpA and found that the transmembrane region must form a critical nucleus comprised of three molecules before undergoing further oligomerization to form large molecular weight species. Finally, we studied the conformation of the unfolded OmpA monomer and found that the folding-competent form of the transmembrane region adopts an expanded conformation, which is in contrast to previous studies that have suggested a collapsed unfolded state.

Interaction with Polyglutamine-expanded Huntingtin Alters Cellular Distribution and RNA Processing of Huntingtin Yeast Two-hybrid Protein A (HYPA)

Huntington disease (HD) is an autosomal inherited disorder that causes the deterioration of brain cells. The polyglutamine (polyQ) expansion of huntingtin (Htt) is implicated in the pathogenesis of HD via interaction with an RNA splicing factor, Htt yeast two-hybrid protein A/forming-binding protein 11 (HYPA/FBP11). Besides the pathogenic polyQ expansion, Htt also contains a proline-rich region (PRR) located exactly in the C terminus to the polyQ tract. However, how the polyQ expansion influences the PRR-mediated protein interaction and how this abnormal interaction leads to the biological consequence remain elusive. Our NMR structural analysis indicates that the PRR motif of Htt cooperatively interacts with the tandem WW domains of HYPA through domain chaperoning effect of WW1 on WW2. The polyQ-expanded Htt sequesters HYPA to the cytosolic location and then significantly reduces the efficiency of pre-mRNA splicing. We propose that the toxic gain-of-function of the polyQ-expanded Htt that causes dysfunction of cellular RNA processing contributes to the pathogenesis of HD.

Aggregation of γ-crystallins associated with human cataracts via domain swapping at the C-terminal β-strands.

The prevalent eye disease age-onset cataract is associated with aggregation of human γD-crystallins, one of the longest-lived proteins. Identification of the γ-crystallin precursors to aggregates is crucial for developing strategies to prevent and reverse cataract. Our microseconds of atomistic molecular dynamics simulations uncover the molecular structure of the experimentally detected aggregation-prone folding intermediate species of monomeric native γD-crystallin with a largely folded C-terminal domain and a mostly unfolded N-terminal domain. About 30 residues including a, b, and c strands from the Greek Key motif 4 of the C-terminal domain experience strong solvent exposure of hydrophobic residues as well as partial unstructuring upon N-terminal domain unfolding. Those strands comprise the domain-domain interface crucial for unusually high stability of γD-crystallin. We further simulate the intermolecular linkage of these monomeric aggregation precursors, which reveals domain-swapped dimeric structures. In the simulated dimeric structures, the N-terminal domain of one monomer is frequently found in contact with residues 135-164 encompassing the a, b, and c strands of the Greek Key motif 4 of the second molecule. The present results suggest that γD-crystallin may polymerize through successive domain swapping of those three C-terminal β-strands leading to age-onset cataract, as an evolutionary cost of its very high stability. Alanine substitutions of the hydrophobic residues in those aggregation-prone β-strands, such as L145 and M147, hinder domain swapping as a pathway toward dimerization. These findings thus provide critical molecular insights onto the initial stages of age-onset cataract, which is important for understanding protein aggregation diseases.

β-connectin studies by small-angle x-ray scattering and single-molecule force spectroscopy by atomic force microscopy

The three-dimensional structure and the mechanical properties of a β-connectin fragment from human cardiac muscle, belonging to the I band, from I(27) to I(34), were investigated by small-angle x-ray scattering (SAXS) and single-molecule force spectroscopy (SMFS). This molecule presents an entropic elasticity behavior, associated to globular domain unfolding, that has been widely studied in the last 10 years. In addition, atomic force microscopy based SMFS experiments suggest that this molecule has an additional elastic regime, for low forces, probably associated to tertiary structure remodeling. From a structural point of view, this behavior is a mark of the fact that the eight domains in the I(27)-I(34) fragment are not independent and they organize in solution, assuming a well-defined three-dimensional structure. This hypothesis has been confirmed by SAXS scattering, both on a diluted and a concentrated sample. Two different models were used to fit the SAXS curves: one assuming a globular shape and one corresponding to an elongated conformation, both coupled with a Coulomb repulsion potential to take into account the protein-protein interaction. Due to the predominance of the structure factor, the effective shape of the protein in solution could not be clearly disclosed. By performing SMFS by atomic force microscopy, mechanical unfolding properties were investigated. Typical sawtooth profiles were obtained and the rupture force of each unfolding domain was estimated. By fitting a wormlike chain model to each peak of the sawtooth profile, the entropic elasticity of octamer was described.

Amyloid-β42 Interacts Mainly with Insoluble Prion Protein in the Alzheimer Brain

The prion protein (PrP) is best known for its association with prion diseases. However, a controversial new role for PrP in Alzheimer disease (AD) has recently emerged. In vitro studies and mouse models of AD suggest that PrP may be involved in AD pathogenesis through a highly specific interaction with amyloid-β (Aβ42) oligomers. Immobilized recombinant human PrP (huPrP) also exhibited high affinity and specificity for Aβ42 oligomers. Here we report the novel finding that aggregated forms of huPrP and Aβ42 are co-purified from AD brain extracts. Moreover, an anti-PrP antibody and an agent that specifically binds to insoluble PrP (iPrP) co-precipitate insoluble Aβ from human AD brain. Finally, using peptide membrane arrays of 99 13-mer peptides that span the entire sequence of mature huPrP, two distinct types of Aβ binding sites on huPrP are identified in vitro. One specifically binds to Aβ42 and the other binds to both Aβ42 and Aβ40. Notably, Aβ42-specific binding sites are localized predominantly in the octapeptide repeat region, whereas sites that bind both Aβ40 and Aβ42 are mainly in the extreme N-terminal or C-terminal domains of PrP. Our study suggests that iPrP is the major PrP species that interacts with insoluble Aβ42 in vivo. Although this work indicated the interaction of Aβ42 with huPrP in the AD brain, the pathophysiological relevance of the iPrP/Aβ42 interaction remains to be established.

A structural basis for Lowe syndrome caused by mutations in the Rab-binding domain of OCRL1

The oculocerebrorenal syndrome of Lowe (OCRL), also called Lowe syndrome, is characterized by defects of the nervous system, the eye and the kidney. Lowe syndrome is a monogenetic X-linked disease caused by mutations of the inositol-5-phosphatase OCRL1. OCRL1 is a membrane-bound protein recruited to membranes via interaction with a variety of Rab proteins. The structural and kinetic basis of OCRL1 for the recognition of several Rab proteins is unknown. In this study, we report the crystal structure of the Rab-binding domain (RBD) of OCRL1 in complex with Rab8a and the kinetic binding analysis of OCRL1 with several Rab GTPases (Rab1b, Rab5a, Rab6a and Rab8a). In contrast to other effectors that bind their respective Rab predominantly via α-helical structure elements, the Rab-binding interface of OCRL1 consists mainly of the IgG-like β-strand structure of the ASPM-SPD-2-Hydin domain as well as one α-helix. Our results give a deeper structural understanding of disease-causing mutations of OCRL1 affecting Rab binding.