Effects Of Single Point Mutations Research Articles

Systems-level response to point mutations in a core metabolic enzyme modulates genotype-phenotype relationship.

Linking the molecular effects of mutations to fitness is central to understanding evolutionary dynamics. Here, we establish a quantitative relation between the global effect of mutations on the E. coli proteome and bacterial fitness. We created E. coli strains with specific destabilizing mutations in the chromosomal folA gene encoding dihydrofolate reductase (DHFR) and quantified the ensuing changes in the abundances of 2,000+ E. coli proteins in mutant strains using tandem mass tags with subsequent LC-MS/MS. mRNA abundances in the same E. coli strains were also quantified. The proteomic effects of mutations in DHFR are quantitatively linked to phenotype: the SDs of the distributions of logarithms of relative (to WT) protein abundances anticorrelate with bacterial growth rates. Proteomes hierarchically cluster first by media conditions, and within each condition, by the severity of the perturbation to DHFR function. These results highlight the importance of a systems-level layer in the genotype-phenotype relationship.

Effective temperature of mutations.

Biological macromolecules experience two seemingly very different types of noise acting on different time scales: (i)point mutations corresponding to changes in molecular sequence and (ii)thermal fluctuations. Examining the secondary structures of a large number of microRNA precursor sequences and model lattice proteins, we show that the effects of single point mutations are statistically indistinguishable from those of an increase in temperature by a few tens of kelvins. The existence of such an effective mutational temperature establishes a quantitative connection between robustness to genetic (mutational) and environmental (thermal) perturbations.

Free energy calculations of A(2A) adenosine receptor mutation effects on agonist binding.

A general computational scheme to evaluate the effects of single point mutations on ligand binding is reported. This scheme is applied to characterize agonist binding to the A2A adenosine receptor, and is found to accurately explain how point mutations of different nature affect the binding affinity of a potent agonist.

Potential Role of Phosphorylation as a Regulator of Aspartyl-(asparaginyl)-β-hydroxylase: Relevance to Infiltrative Spread of Human Hepatocellular Carcinoma

Abundant expression of aspartyl-(asparaginyl)-β-hydroxylase (AAH) correlates with infiltrative growth of hepatocellular carcinoma (HCC). Herein, we examine the role of phosphorylation in relation to AAH's protein expression, hydroxylase activity, promotion of cell motility, and activation of Notch signaling in human Huh7 hepatoma cells. Predicted glycogen synthase kinase-3β (GSK-3β) , protein kinase A (PKA), protein kinase C (PKC), and casein kinase 2 (CK2) phosphorylation sites encoded by human AAH cDNA were ablated by S/T→A site-directed mutagenesis using N-Myc-tagged constructs in which gene expression was controlled by a cytomegalovirus promoter. Functional consequences were assessed in transiently transfected Huh7 cells. Cells transfected with wildtype AAH had significantly increased AAH expression, catalytic activity, HES-1 expression, and directional motility relative to controls. Single phosphorylation site mutations in the C-terminus largely abrogated these effects and further inhibited catalytic activity relative to that in cells transfected with empty vector, whereas the effects of single point mutations within the N-terminus were more varied. In contrast, AAH cDNAs carrying multiple phosphorylation site mutations exhibited wildtype levels of AAH catalytic activity suggesting that the effects of AAH phosphorylation are complex and non-uniform. AAH expression and function can be modulated by direct phosphorylation of the protein. These findings suggest additional strategies for inhibiting infiltrative growth of HCC.

Tetramerization-defects of p53 result in aberrant ubiquitylation and transcriptional activity

The tumor suppressor p53 regulates the expression of genes involved in cell cycle progression, senescence and apoptosis. Here, we investigated the effect of single point mutations in the oligomerization domain (OD) on tetramerization, transcription, ubiquitylation and stability of p53. As predicted by docking and molecular dynamics simulations, p53 OD mutants show functional defects on transcription, Mdm2-dependent ubiquitylation and 26S proteasome-mediated degradation. However, mutants unable to form tetramers are well degraded by the 20S proteasome. Unexpectedly, despite the lower structural stability compared to WT p53, p53 OD mutants form heterotetramers with WT p53 when expressed transiently or stably in cells wild type or null for p53. In consequence, p53 OD mutants interfere with the capacity of WT p53 tetramers to be properly ubiquitylated and result in changes of p53-dependent protein expression patterns, including the pro-apoptotic proteins Bax and PUMA under basal and adriamycin-induced conditions. Importantly, the patient derived p53 OD mutant L330R (OD1) showed the more severe changes in p53-dependent gene expression. Thus, in addition to the well-known effects on p53 stability, ubiquitylation defects promote changes in p53-dependent gene expression with implications on some of its functions.

Transmission line model analysis of transcription factors binding to oligoduplexes – differentiation of the effect of single nucleotide modifications

Advanced impedance spectroscopy analysis based on the transmission line model (TLM) is explored as a novel QCM acoustic biosensing platform for the detection of the single point mutation effect on the binding of the transcription factors (TFs) to immobilized DNA oligoduplexes and the characterization of the protein-DNA mechanical properties.

Structural Elucidation of Unique Inhibitory Activities of Two Thiazolo[ 4,5-d]pyrimidines Against Epidermal Growth Factor Receptor (EGFR): Implications for Successful Drug Design

In our previous study, a protein engineering approach, accounting for the effects of single point mutations of the binding site residues on the stability of 22 thiazolo[4,5-d]pyrimidines in complex with the intracellular kinase domain of EGFR (PDB ID: 1XKK), was established in a systematic manner to be an efficient strategy for the identification of anti-EGFR-related-cancer drug candidates. The inhibitory activities of two lignad molecules, 4-(7-(3-chloro-4-morpholinophenylamino)thiazolo[4,5-d]pyrimidin-2-ylamino)benzenesulfonamide and 4-(7-(4-morpholinophenylamino) thiazolo[4,5-d]pyrimidin-2-ylamino)benzenesulfonamide, exhibited some sort of uniqueness. Regardless of a slight mutual structural difference between these two ligands in only a peripheral Cl atom, their inhibitory activities against EGFR appeared to be associated with two quite opposite structural bases respectively. Herein, the fundamental rationalization of the remarkable standpoint is elaborated using both molecular docking and molecular dynamics simulations. Consequently, a number of implications of vital importance for the successful structure-based design of prospective drugs against EGFR-related cancers are discussed.

Effect of single-point mutations on the stability and immunogenicity of a recombinant ricin A chain subunit vaccine antigen

There is great interest in the design and development of highly thermostable and immunogenic protein subunit vaccines for biodefense. In this study, we used two orthogonal and complementary computational protein design approaches to generate a series of single-point mutants of RiVax, an attenuated recombinant ricin A chain (RTA) protein subunit vaccine antigen. As assessed by differential scanning calorimetry, the conformational stabilities of the designed mutants ranged from 4°C less stable to 4.5°C more stable than RiVax, depending on solution pH. Two more thermostable (V18P, C171L) and two less thermostable (T13V, S89T) mutants that displayed native-like secondary and tertiary structures (as determined by circular dichroism and fluorescence spectral analysis, respectively) were tested for their capacity to elicit RTA-specific antibodies and toxin-neutralizing activity. Following a prime-boost regimen, we found qualitative differences with respect to specific antibody titers and toxin neutralizing antibody levels induced by the different mutants. Upon a second boost with the more thermostable mutant C171L, a statistically significant increase in RTA-specific antibody titers was observed when compared with RiVax-immunized mice. Notably, the results indicate that single residue changes can be made to the RiVax antigen that increase its thermal stability without adversely impacting the efficacy of the vaccine.

Inferring PDZ Domain Multi-Mutant Binding Preferences from Single-Mutant Data

Many important cellular protein interactions are mediated by peptide recognition domains. The ability to predict a domain's binding specificity directly from its primary sequence is essential to understanding the complexity of protein-protein interaction networks. One such recognition domain is the PDZ domain, functioning in scaffold proteins that facilitate formation of signaling networks. Predicting the PDZ domain's binding specificity was a part of the DREAM4 Peptide Recognition Domain challenge, the goal of which was to describe, as position weight matrices, the specificity profiles of five multi-mutant ERBB2IP-1 domains. We developed a method that derives multi-mutant binding preferences by generalizing the effects of single point mutations on the wild type domain's binding specificities. Our approach, trained on publicly available ERBB2IP-1 single-mutant phage display data, combined linear regression-based prediction for ligand positions whose specificity is determined by few PDZ positions, and single-mutant position weight matrix averaging for all other ligand columns. The success of our method as the winning entry of the DREAM4 competition, as well as its superior performance over a general PDZ-ligand binding model, demonstrates the advantages of training a model on a well-selected domain-specific data set.

Using Statistically Significant Correlated Motions of Residues in a MD Based Approach to Investigate Allostery in Ubiquitin Conjugating Protein

Ubiquitin conjugating proteins (E2s) are an important component of the ubiquitin proteasome pathway. E2s interact with ubiquitin activating enzyme (E1) and ubiquitin ligases (E3s) to transfer ubiquitin to target proteins to mark them for degradation. In some E3s, RING domains act as scaffolds to bind E2s and target proteins so that the ubiquitin can be directly transferred from the E2 to the target protein. This ubiquitin transfer has been shown to be allosterically regulated: E3 RING domain binding to E2 at one site promotes ubiquitin release from the active site cysteine (∼15Å distance) without substantial conformational change in E2. Previous studies used statistical coupling analysis (SCA) to identify clusters of residues that might transmit information. Here, we use a novel information-theory approach to identify residues with statistically significant correlated conformations in a set of equilibrium molecular dynamics simulations. From the matrix of correlations between residues, we observed substantial coupling between an E2's active site and its E3 RING domain binding site. However, in the I88A mutant, the pattern of correlations is disrupted, consistent with the experimental observation that this I88A mutation abrogates the allostery in the E2s. Thus, our approach is sensitive enough to identify effects of single point mutations in the protein. Unlike SCA, which infers couplings from many protein sequences, our approach identifies couplings between residues in individual proteins, some of which coincide with residues identified by SCA. As our approach is general and sensitive to small physical-chemical differences in sequence, structure, and dynamics, we can apply our approach to study similarities and differences in the allosteric networks of different E2s in order to better understand how protein degradation is regulated, also providing a mechanistic insight of the process.

Glanzmann Mutations : New Allelic Variants and Role of the β3 Lys253 in the αIIb/β3 Interaction Highlighted by the Lys253Met Substitution.

Abstract 1312Poster Board I-336 IntroductionGlanzmann thrombasthenia (GT) is an autosomal recessive inherited bleeding disorder characterized by an impaired platelet aggregation. GT results from defects of the platelet fibrinogen receptor αIIbβ3. GT mutations provide useful tools for structure-function relationship studies of αIIbβ3. Patient and methodsGenomic DNA from 6 patients has been amplified for αIIb and β3 promoters and exons sequences. PCR products were directly sequenced. Potential RNA processing alterations have been studied in silico by using Genscan, NNSPLICE and ESEFinder online tools. When no RNA splicing anomaly was predicted, the effect of single point mutation on αIIbβ3 expression has been studied by using transiently transfected Cos cells. Finally, structural consequences of amino acid substitutions has been studied using the published model of αIIbβ3 (code PDB 2VDL) and structural modelling. Results7 new mutations have been characterized. 1 deletion / insertion, 2 single point mutations inducing stop codon and 1 resulting in splicing site disruption were identified. The 3 last identified single point mutations were not predicted to affect normal RNA processing but has been shown to prevent normal expression of mutant αIIbβ3 at the surface of Cos cells. The p.Meth118Arg and p.Gly221Asp substitutions that induce both important steric hindrance and charge modifications, are located inside the β-I domain of β3. So they should deeply alter the proper folding of the β-I domain, preventing the complex expression at the platelet surface. On the other hand, the p.Lys253Met protrudes from the β-I domain toward the αIIb β-propeller. A structural model of the Met253 β-I mutant has been done. An estimation of the direct electrostatic and desolvation free energies of interaction between the β-I domain surface and the αIIb β-propeller indicated that rather than the presence of a methionine, it is the lost of the Lys253 which is responsible for the complex expression defect. ConclusionSeven new GT mutations have been identified and the p.Lys253Met substitution helped to define a key role of the Lys253 in the αIIb β-propeller / β3 β-I domains interaction. DisclosuresNo relevant conflicts of interest to declare.

Insights into Human β-Cardiac Myosin Function from Single Molecule and Single Cell Studies

beta-Cardiac myosin is a mechanoenzyme that converts the energy from ATP hydrolysis into a mechanical force that drives contractility in muscle. Thirty percent of the point mutations that result in hypertrophic cardiomyopathy are localized to MYH7, the gene encoding human beta-cardiac myosin heavy chain (beta-MyHC). Force generation by myosins requires a tight and highly conserved allosteric coupling between its different protein domains. Hence, the effects of single point mutations on the force generation and kinetics of beta-cardiac myosin molecules cannot be predicted directly from their location within the protein structure. Great insight would be gained from understanding the link between the functional defect in the myosin protein and the clinical phenotypes of patients expressing them. Over the last decade, several single molecule techniques have been developed to understand in detail the chemomechanical cycle of different myosins. In this review, we highlight the single molecule techniques that can be used to assess the effect of point mutations on beta-cardiac myosin function. Recent bioengineering advances have enabled the micromanipulation of single cardiomyocyte cells to characterize their force-length dynamics. Here, we briefly review single cell micromanipulation as an approach to determine the effect of beta-MyHC mutations on cardiomyocyte function. Finally, we examine the technical challenges specific to studying beta-cardiac myosin function both using single molecule and single cell approaches.

The consequences of pathogenic mutations to the human prion protein.

Prion diseases, in which the conformational transition of the native prion protein (PrP) to a misfolded form causes aggregation and subsequent neurodegeneration, have fascinated the scientific community as this transmissible disease appears to be purely protein-based. Disease can arise due to genetic factors only. At least 30 single point mutations have been indicated to cause disease in humans. Somehow, these mutations must influence the stability, processing and/or cellular interactions of PrP, such that aggregation can occur and disease develops. In this review, the current evidence for such effects of single point mutations is discussed, indicating that PrP can be affected in many different ways, although questions remain about the mechanism by which mutations cause disease.

Structural Elements Regulating Amyloidogenesis: A Cholinesterase Model System

Polymerization into amyloid fibrils is a crucial step in the pathogenesis of neurodegenerative syndromes. Amyloid assembly is governed by properties of the sequence backbone and specific side-chain interactions, since fibrils from unrelated sequences possess similar structures and morphologies. Therefore, characterization of the structural determinants driving amyloid aggregation is of fundamental importance. We investigated the forces involved in the amyloid assembly of a model peptide derived from the oligomerization domain of acetylcholinesterase (AChE), AChE586-599, through the effect of single point mutations on β-sheet propensity, conformation, fibrilization, surfactant activity, oligomerization and fibril morphology. AChE586-599 was chosen due to its fibrilization tractability and AChE involvement in Alzheimer's disease. The results revealed how specific regions and residues can control AChE586-599 assembly. Hydrophobic and/or aromatic residues were crucial for maintaining a high β-strand propensity, for the conformational transition to β-sheet, and for the first stage of aggregation. We also demonstrated that positively charged side-chains might be involved in electrostatic interactions, which could control the transition to β-sheet, the oligomerization and assembly stability. Further interactions were also found to participate in the assembly. We showed that some residues were important for AChE586-599 surfactant activity and that amyloid assembly might preferentially occur at an air-water interface. Consistently with the experimental observations and assembly models for other amyloid systems, we propose a model for AChE586-599 assembly in which a steric-zipper formed through specific interactions (hydrophobic, electrostatic, cation-π, SH-aromatic, metal chelation and polar-polar) would maintain the β-sheets together. We also propose that the stacking between the strands in the β-sheets along the fiber axis could be stabilized through π-π interactions and metal chelation. The dissection of the specific molecular recognition driving AChE586-599 amyloid assembly has provided further knowledge on such poorly understood and complicated process, which could be applied to protein folding and the targeting of amyloid diseases.

Point Mutations in Membrane Proteins Reshape Energy Landscape and Populate Different Unfolding Pathways

Using single-molecule force spectroscopy, we investigated the effect of single point mutations on the energy landscape and unfolding pathways of the transmembrane protein bacteriorhodopsin. We show that the unfolding energy barriers in the energy landscape of the membrane protein followed a simple two-state behavior and represent a manifestation of many converging unfolding pathways. Although the unfolding pathways of wild-type and mutant bacteriorhodopsin did not change, indicating the presence of same ensemble of structural unfolding intermediates, the free energies of the rate-limiting transition states of the bacteriorhodopsin mutants decreased as the distance of those transition states to the folded intermediate states decreased. Thus, all mutants exhibited Hammond behavior and a change in the free energies of the intermediates along the unfolding reaction coordinate and, consequently, their relative occupancies. This is the first experimental proof showing that point mutations can reshape the free energy landscape of a membrane protein and force single proteins to populate certain unfolding pathways over others.

Effects of Single Point Mutations within Proposed Copper Binding Sites on Specific Activity and Inter-Chain Affinity of Factor VIII.

Copper ions appear important for the structural integrity and the function of factor VIII. Reconstitution studies have shown that Cu2+ increases specific activity of factor VIII as well as increases affinity between heavy chain (HC) and light chain (LC). Based on the ceruloplasmin homology, the existence of three Cu2+ binding sites has been proposed. These include a type 1 site in HC (A1 domain) coordinated by C310, H315, H267, and M320, a type 1 site in LC (A3 domain) coordinated by C2000, H1954, H2005, and M2010, and type 2 site spanning A1 and A3 domains coordinated by H99 and H1957 with possible other additional residues. We rationalized that point mutations within a putative Cu2+ coordination sites would diminish Cu2+ binding at that site, as detected by changes in factor VIII specific activity and/or inter-subunit affinity. We produced several mutant factor VIII proteins bearing point mutation of C310S, H315A, C2000S, H1954A, H99A, or H1957A using a B-domainless human factor VIII vector. Each mutant was stably expressed and purified by SP-sepharose, which bound factor VIII primarily though LC. Western blotting indicated a reduction in the relative amount of HC in C310S and H99A factor VIII forms, suggesting that inter-chain affinity was reduced by these mutations. EDTA-treated factor VIII forms in the presence of Ca2+ were titrated with Cu2+ and activity was monitored using a factor Xa generation assay. The concentration of free Cu2+ was controlled by the presence of EDTA and Ca2+ based on the known values for Cu2+-EDTA and Ca2+-EDTA affinities. The activity regain observed for wild type factor VIII following titration with Cu2+ yielded a Kd = 11.5 ± 2.2 fM. All of the mutants tested retained a high affinity response to Cu2+, suggesting that single point mutations were not sufficient to eliminate Cu2+ binding. However, while Kd values for H1957A (10.3 ± 2.2 fM), H99A (2.1 ± 1.9 fM), H315A (6.7 ± 3.1 fM), and C310S (12.7 ± 3.4 fM) retained similar or slightly reduced affinity for Cu2+, the Kd values for C2000S (304 ± 105 fM) and H1954A (365 ± 105 fM) showed a significant reduction in Cu2+ affinity. When factor VIIIa subunits were titrated with Cu2+ and monitored by intrinsic fluorescence, only purified A1 subunit showed a saturable effect of the signal (Kd = 11.9 ± 4.9 fM), indicating that this subunit contained a high affinity Cu2+ binding site. Taken together, these results suggest that occupancy of the type 1 Cu2+ binding site in A3 contributes to the Cu2+-dependent increase in specific activity of factor VIII and that the type 1 site in A1 and/or the type 2 site contributes to HC-LC association.

Correlation of Local Changes in the Temperature-Dependent Conformational Flexibility of Thioredoxins with Their Thermostability

For the development of a method capable of predicting single point mutations substantially affecting protein thermostability, we studied the effect of the E85R and R82E mutations on the thermostability of thioredoxins from Escherichia coli (Trx) andBacillus acidocaldarius (BacTrx), respectively. The basic method of investigation was the molecular dynamics simulation of 3D protein models in an explicit solvent at different temperatures (300 and 373 K). Some thermolabile regions in Trx, BacTrx, and their mutants were revealed by analyzing the temperature effect on the molecular dynamics of the protein molecule. The effect of single point mutations on the temperature changes of the protein conformation flexibility in several thermolabile regions was found. The results of the simulations are in accord with experimental data indicating that the mutation E85R increases Trx thermostability, whereas the mutation R82E decreases BacTrx thermostability. The thermostability of these proteins was revealed to depend on ionic interactions between the thermolabile regions. The single point mutations change the parameters of these interactions and make them more favorable in the E85R-Trx mutant and less favorable in the R82E-BacTrx mutant.

Electrostatic interactions across the dimer–dimer interface contribute to the pH-dependent stability of a tetrameric malate dehydrogenase

Malate dehydrogenase (MDH) from the moderately thermophilic bacterium Chloroflexus aurantiacus (CaMDH) is a tetrameric enzyme, while MDHs from mesophilic bacteria usually are dimers. Using site-directed mutagenesis, we show here that a network of electrostatic interactions across the extra dimer–dimer interface in CaMDH is important for thermal stability and oligomeric integrity. Stability effects of single point mutations (E25Q, E25K, D56N, D56K) varied from −1.2°C to −26.8°C, and depended strongly on pH. Gel-filtration experiments indicated that the 26.8°C loss in stability observed for the D56K mutant at low pH was accompanied by a shift towards a lower oligomerization state.

In Silico Structure-based Design of a Potent, Mutation Resilient, Small Peptide Inhibitor of HIV-1 Reverse Transcriptase

A crucial step in the replication of HIV-1 is the conversion of its single-stranded RNA to double-stranded DNA, which is catalyzed by the virally encoded reverse transcriptase (RT). The latter is therefore a key target for the development of anti-HIV drugs. Currently approved anti- RT drugs fall into two main classes: (i) nucleoside analog inhibitors which are incorporated into the primer strand in their metabolically activated triphosphate forms, causing termination of DNA synthesis due to their 3′-deoxy configuration and (ii) the non-nucleoside inhibitors (NNIs), which are generally specific for HIV-1 RT and bind at an allosteric site approximately 10 Å from the active site causing a displacement of the catalytic aspartate residues. The so- called “first generation” NNI drugs are generally susceptible to the effects of single-point mutations within RT, while more recent “second generation” NNIs, such as efavirenz, the car- boxanilide UC-781 and certain quinoxalines demonstrate much greater resilience to mutations in RT. The crystal structures of the complexes of wild type and mutant RTs with first and second generation NNIs have shown that, for an inhibitor to be potent as well as mutation resilient, it should (i) make hydrogen bonds with the main chain of RT, (ii) have a large number of interactions with RT and (iii) have the ability to rearrange and adapt to a mutated NNI pocket. Based on the crystal structures of the complexes of wild type RT and Tyr188Cys mutant of RT with UC-781, we have designed a small peptide inhibitor. Docking results on this peptide using AutoDock3.0 and SYBYL 6.8.1 indicate that the peptide has a potency comparable to that of UC-781 with a retention of activity against the Tyr188Cys mutant RT. The proposed, small peptide is seen to possess all the desirable features of a potent and mutation resilient inhibitor and is hence a potential lead compound.

Protein concerted motions in the DNA-human topoisomerase I complex.

The collective motions of the core and C-terminal domains of human topoisomerase I (topo I) have been analysed by molecular dynamics simulation of the protein in covalent complex with a 22 bp DNA duplex. The analysis evidenced a great number of correlated movements of core subdomain I and II residues, and a central role for helix 5 in the protein-DNA communication, in particular with the scissile strand downstream of the cleavage site. The flow of information between these core subdomains and DNA suggests that subdomains I and II play an essential role in the DNA relaxation process. In core subdomain III the majority of DNA contacting residues do not communicate with protein regions far from DNA, suggesting that they have a structural role. However, selected core subdomain III residues, involved in the orientation of the active site region, show correlated movements with residues distant from DNA, indicating that the information concerning the catalytic event is also transmitted. The flexibility of two loops formed by residues 519-520 and 580-584 seems indispensable to the dynamic participation of core subdomain III to the DNA cleavage and religation steps. The motion of specific residues has also been found to explain the effect of single point mutations that make topo I resistant to the anticancer drug camptothecin.