Subtle Structural Changes Research Articles

Subtle Structural Change in the Exciton-Forming Dye Drives Plasmon–Exciton Interaction Involving Gold Nanorods into the Strong Coupling Regime: Implications for Enhanced Optical Processes

Subtle Structural Change in the Exciton-Forming Dye Drives Plasmon–Exciton Interaction Involving Gold Nanorods into the Strong Coupling Regime: Implications for Enhanced Optical Processes

Simulation study of the effects of polymer network dynamics and mesh confinement on the diffusion and structural relaxation of penetrants.

The diffusion of small molecular penetrants through polymeric materials represents an important fundamental problem, relevant to the design of materials for applications such as coatings and membranes. Polymer networks hold promise in these applications because dramatic differences in molecular diffusion can result from subtle changes in the network structure. In this paper, we use molecular simulation to understand the role that cross-linked network polymers have in governing the molecular motion of penetrants. By considering the local, activated alpha relaxation time of the penetrant and its long-time diffusive dynamics, we can determine the relative importance of activated glassy dynamics on penetrants at the segmental scale vs entropic mesh confinement on penetrant diffusion. We vary several parameters, such as the cross-linking density, temperature, and penetrant size, to show that cross-links primarily affect molecular diffusion through the modification of the matrix glass transition, with local penetrant hopping at least partially coupled to the segmental relaxation of the polymer network. This coupling is very sensitive to the local activated segmental dynamics of the surrounding matrix, and we also show that penetrant transport is affected by dynamic heterogeneity at low temperatures. To contrast, only at high temperatures and for large penetrants or when the dynamic heterogeneity effect is weak, does the effect of mesh confinement become significant, even though penetrant diffusion more broadly empirically follows similar trends as established models of mesh confinement-based transport.

Interactions of coumarin and amine ligands with six cytochrome P450 2D6 allelic variants: Molecular docking

Human CYP2D6 contributes extensively to the biotransformation of important therapeutic drugs. CYP2D6 substrate and inhibitor specificity may be affected by genetic polymorphism. This study aimed to characterize interactions of three typical ligands, 3-cyano-7-ethoxycoumarin, fluoxetine and terbinafine with six CYP2D6 variants using molecular docking simulations. The compounds were docked individually to the CYP2D6 models based on published crystal structure (PDB code: 3TBG). All ligands bound within the active site pocket near the heme. Binding involved residues found in critical secondary structures that formed the active site boundary: B-C loop, F helix, F-G loop, β-1 strands and I helix. Twenty-five amino acids were involved in the binding, and all were located in the known substrate recognition sites. Hydrophobic bonds involving phenylalanine (Phe120, Phe384) dominated CEC binding whereas electrostatic bonds between the protonated nitrogen with acidic residues (Glu216, Glu222, Asp301) dominated in binding of fluoxetine and terbinafine. Collectively, the subtle structural changes in the active site and substrate access channels induced by the mutations in the variants contributed to differential ligand docking poses. This study has provided insights into important molecular properties for CYP2D6 catalysis and inhibition, and formed basis for further exploration of structural determinants for potency and specificity of CYP2D6 ligands.

Asp179 in the class A β-lactamase from Mycobacterium tuberculosis is a conserved yet not essential residue due to epistasis.

Conserved residues are often considered essential for function, and substitutions in such residues are expected to have a negative influence on the properties of a protein. However, mutations in a few highly conserved residues of the β-lactamase from Mycobacterium tuberculosis, BlaC, were shown to have no or only limited negative effect on the enzyme. One such mutant, D179N, even conveyed increased ceftazidime resistance upon bacterial cells, while displaying good activity against penicillins. The crystal structures of BlaC D179N in resting state and in complex with sulbactam reveal subtle structural changes in the Ω-loop as compared to the structure of wild-type BlaC. Introducing this mutation in four other β-lactamases, CTX-M-14, KPC-2, NMC-A and TEM-1, resulted in decreased antibiotic resistance for penicillins and meropenem. The results demonstrate that the Asp in position 179 is generally essential for class A β-lactamases but not for BlaC, which can be explained by the importance of the interaction with the side chain of Arg164 that is absent in BlaC. It is concluded that Asp179 though conserved is not essential in BlaC, as a consequence of epistasis.

Structural and magnetic interplay in multiferroic Ho0.5Nd0.5Fe3(BO3)4

Rare-earth iron borates, $R{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ ($R$ = rare earth), are of considerable interest because of their structural and magnetic complexities due to the involvement of both $3d$ and $4f$ magnetic interactions in a helical lattice. Among them ${\mathrm{Ho}}_{0.5}{\mathrm{Nd}}_{0.5}{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ has attracted the most attention, as it exhibits a multiferroic property with a large, spontaneous, and magnetic-field-induced electric polarization ($P$) below the antiferromagnetic transition temperature (${\mathrm{T}}_{N}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}32$ K). This compound has been reported to be noncentrosymmetric (nonpolar) down to the lowest temperature, and the origin of spontaneous electric polarization below ${\mathrm{T}}_{N}$ is not known. By utilizing temperature-dependent synchrotron x-ray powder diffraction, we report here the observation of structural phase transition, i.e., the lowering of crystal symmetry from $R32$ to $P{3}_{1}21$ below ${\mathrm{T}}_{N}$ in ${\mathrm{Ho}}_{0.5}{\mathrm{Nd}}_{0.5}{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$, which is further confirmed by single-crystal x-ray diffraction measurements as well as substantiated by dielectric and Raman spectroscopic results. With the help of x-ray resonant magnetic scattering, we have studied the element-specific magnetic ordering behavior, and by combining all the results, we show that the spontaneous electric polarization below the antiferromagnetic ordering transition emerges through the p-d hybridization mechanism associated with the ${\mathrm{FeO}}_{6}$ octahedra. The observations of subtle structural changes at low temperature and element-specific magnetic ordering behavior provide a comprehensive understanding of the multiferroicity in this family of compounds.

Interfacial Engineering of Block Copolymer Nanostructures: Morphology and Solvent Stability.

Interfacial engineering is a critical pathway for modulating the self-assembled nanostructures of block copolymers (BCPs) during solvent exchange. Herein, we demonstrated the generation of different stacked lamellae of polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP) nanostructures during solvent exchange by using phosphotungstic acid (PTA) or PTA/NaCl aqueous solution as the nonsolvent. The participation of PTA in the confined microphase separation of PS-b-P2VP in droplets increases the volume fraction of P2VP and decreases the tension at the oil/water interface. Moreover, the addition of NaCl to the PTA solution can further increase the surface coverage of P2VP/PTA on droplets. All factors impact the morphology of assembled BCP nanostructures. In the presence of PTA, ellipsoidal particles composed of alternatively stacked lamellae of PS and P2VP were formed (named BP), whereas, in the coexistence of PTA and NaCl, they changed to stacked disks with PS-core-P2VP-shell (called BPN). The different structures of assembled particles induce their different stabilities in solvents and different dissociation conditions as well. The dissociation of BP particles was easy because PS chains were only entangled together which can be swollen in toluene or chloroform. However, the dissociation of BPN was hard, requiring an organic base in hot ethanol. The structural difference in BP and BPN particles further extended to their dissociated disks, which makes the cargo (like R6G) loaded on these disks to show a different stability in acetone. This study demonstrated that a subtle structural change can greatly affect their properties.

Discovery of extended product structural space of the fungal dioxygenase AsqJ

The fungal dioxygenase AsqJ catalyses the conversion of benzo[1,4]diazepine-2,5-diones into quinolone antibiotics. A second, alternative reaction pathway leads to a different biomedically important product class, the quinazolinones. Within this work, we explore the catalytic promiscuity of AsqJ by screening its activity across a broad range of functionalized substrates made accessible by solid-/liquid-phase peptide synthetic routes. These systematic investigations map the substrate tolerance of AsqJ within its two established pathways, revealing significant promiscuity, especially in the quinolone pathway. Most importantly, two further reactivities leading to new AsqJ product classes are discovered, thus significantly expanding the structural space accessible by this biosynthetic enzyme. Switching AsqJ product selectivity is achieved by subtle structural changes on the substrate, revealing a remarkable substrate-controlled product selectivity in enzyme catalysis. Our work paves the way for the biocatalytic synthesis of diverse biomedically important heterocyclic structural frameworks.

Tackling the kinetic dilemma of thioacetals in sensing of mercury through subtle structural changes of S to O

Novel fluorescent probes for Hg2+ are developing rapidly because Hg2+ has serious harm to the human health and natural environment. The deprotection reaction of thioacetal or thioketal based on sulfhydryl group is selective but slow. How to improve the reaction speed of deprotection methods on the premise of ensuring selectivity becomes a key problem. Herein, we designed and synthesized two coumarin ketal probes with similar structures: DTK and MTK. Both probes with highly similar structures could sense Hg2+, but sensing performance was special different. MTK replaced S with O in DTK, resulting in a sharp reduction in detection time (DTK took 18 min, while MTK achieved instantaneous detection of Hg2+), and has excellent sensitivity and selectivity. Moreover, a paper-based sensor was also designed as a convenient real-time device to detect Hg2+.

Investigating the symptomatic and morphological changes in the brain based on pre and post-treatment: A critical review from clinical to neuroimaging studies on schizophrenia.

Pharmacological treatment for schizophrenia has been a long-standing concern. As a severe neuropsychological illness, schizophrenia is always a challenging disorder to unravel its pathophysiology. Since it exhibits both positive and negative symptoms, such as hallucination and delusion, as well as social isolation and cognitive impairment, following the symptomatic changes is a crucial task for clinicians. Although various pharmacological treatments are available in the form of antipsychotics, however, their actual consequences need to be examined with the observable changes in symptoms as well as the unobservable changes in brain functioning. This study is a first of its kind to critically investigate both clinical and neuroimaging studies to find out the changes being observed in schizophrenia patients after clinical intervention with various antipsychotics. We observed several symptomatic changes being reported in clinical studies incorporating clinical trials of various first-generation and second-generation antipsychotic drugs. Alongside, we encapsulated several neuroimaging studies showing functional and structural changes in the brain of schizophrenia patients triggered by a variety of drugs. The basal ganglia, frontal lobe, temporal lobe, cuneus, and middle occipital gyrus are some of the notable brain regions that were observed to show subtle functional and structural changes. This critical review paper may pave the way for future research into the study of the pathological and morphological changes in the brains of schizophrenia patients as they progress through the course of medicinal therapy.

Binding effects of piceatannol and oxyresveratrol on the structural and functional properties of soy protein isolate

Piceatannol (PIC), oxyresveratrol (OXY), and soy protein isolate (SPI) are essential dietary molecules. This study evaluated the interaction between PIC/OXY and SPI using multiple spectroscopic techniques and molecular docking simulations. The static quenching mechanism was confirmed by steady-state fluorescence, Förster resonance energy transfer (FRET), and time-resolved fluorescence (TRF) spectroscopy. The binding affinity of PIC to SPI was stronger than that of OXY, and the interactions were spontaneous and exothermic. The subtle change in the secondary structure of SPI after the addition of PIC or OXY can be ascertained by analyzing the surface hydrophobicity, sulfhydryl group content, particle size, zeta potential, and α-helical content. The emulsifying and foaming properties of SPI were enhanced after complexing with PIC/OXY. The thermodynamic parameters and molecular docking results demonstrated that PIC and OXY bound to SPI at the same sites, and that van der Waals forces (vdW forces) and hydrogen bonding (H-bonding) were the main interaction forces. In addition, the results also showed that the encapsulation of SPI can enhance the antioxidant activity of PIC and OXY. The in vitro gastrointestinal digestion of PIC and OXY in the absence or presence of SPI was evaluated. This study can be used as a reference for further research on the digestion and absorption of SPI−PIC/OXY complexes and as a guide for healthy diets.

Concentration‐Induced Hetero‐Valent Partial‐Inverse Occupation of Infrared Phosphor

AbstractInfrared luminescent materials have evoked much attention from chemists and material scientists. Although substantial progress is made in materials design, the luminescent mechanism remains ambiguous in the complex structures, presenting major barriers to developing novel infrared luminescent materials. Herein, this study aims to deliberate a complete discussion on infrared phosphors with concentration‐induced hetero‐valent partial‐inverse occupation. High‐resolution synchrotron X‐ray diffraction and Raman spectroscopy reveal the subtle structural change in LiGa5(1−x)O8:5xCr3+. Besides, Cr K‐edge wavelet analysis and extended X‐ray absorption fine structure illustrate the impact of Cr in the second shell of another Cr ion and the practical coordination of Ga and Cr ions. Furthermore, unexpected two‐center Cr3+emissions and the Cr–Cr pair emission are observed at high Cr concentrations. Variation between the zero‐phonon line and N‐line at different temperatures is demonstrated. Finally, the structural and luminescent properties are comprehensively discussed, providing the origin of the unexpected Cr2 emission. This study not only provides insight into the hetero‐valent partial‐inverse occupation process in inorganic materials but also sheds light on developing novel infrared luminescent materials.

Raman study of pressure-induced phase transitions in imidazolium manganese- hypophosphite hybrid perovskite

By using Raman spectroscopy, we demonstrate that [IM]Mn(H2POO)3 is a highly compressible material that undergoes three pressure-induced phase transitions. Using a diamond anvil cell we performed high-pressure experiments up to 7.1 GPa, using paraffin oil as the compression medium. The first phase transition, which occurs near 2.9 GPa, leads to very pronounced changes in the Raman spectra. This behavior indicates that this transition is associated with very large reconstruction of the inorganic framework and collapse of the perovskite cages. The second phase transition, which occurs near 4.9 GPa, is associated with subtle structural changes. The last transition takes place near 5.9 GPa and it leads to further significant distortion of the anionic framework. In contrast to the anionic framework, the phase transitions have weak impact on the imidazolium cation. Pressure dependence of Raman modes proves that compressibility of the high-pressure phases is significantly lower compared to the ambient pressure phase. It also indicates that the contraction of the MnO6 octahedra prevails over that of the imidazolium cations and hypophosphite linkers. However, compressibility of MnO6 strongly decreases in the highest pressure phase. Pressure-induced phase transitions are reversible.

Actin's C-terminus coordinates actin structural changes and functions.

Actin is essential to eukaryotic cellular processes. Actin's C-terminus appears to play a direct role in modulating actin's structure and properties, facilitating the binding and function of actin-binding proteins (ABPs). The structural and functional characterization of filamentous actin's C-terminus has been impeded by its inherent flexibility, as well as actin's resistance to crystallization for x-ray diffraction and the historical resolution constraints associated with electron microscopy. Many biochemical studies have established that actin's C-terminus must retain its flexibility and structural integrity to modulate actin's structure and functions. For example, C-terminal structural changes are known to affect nucleotide binding and exchange, as well as propagate actin structural changes throughout extensive allosteric networks, facilitating the binding and function of ABPs. Advances in electron microscopy have resulted in high-resolution structures of filamentous actin, providing insights into subtle structural changes that are mediated by actin's C-terminus. Here, we review existing knowledge establishing the importance of actin's C-terminus within actin structural changes and functions and discuss how modern structural characterization techniques provide the tools to understand the role of actin's C-terminus in cellular processes.

Gradual evolution of hydrogen-bonding patterns with the carbamoylcyanonitrosomethanide anion in a series of aliphatic diammonium salts.

Developing the structures of organic materials that rely on the hydrogen bonding of multifunctional substrates is often complicated due to a competition between various possible motifs. In this context, the illustrative case of the carbamoylcyanonitrosomethanide anion, [ONC(CN)-C(O)NH2]-, suggests sufficient control over the crystal lattice with a set of supramolecular synthons, which are specific to all the present nitroso, carbamoyl and cyano groups. The structures of the carbamoylcyanonitrosomethanide salts of ethane-1,2-diammonium, C2H10N22+·2C3H2N3O2-, (1), piperazine-1,4-diium, C4H12N22+·2C3H2N3O2-, (2), butane-1,4-diammonium, C4H14N22+·2C3H2N3O2-, (3), and hexane-1,6-diammonium, C6H18N22+·2C3H2N3O2-, (4), reveal two- and three-dimensional hydrogen-bonded frameworks governed by a set of site-selective interactions. The strongest N-H...O hydrogen bonds [N...O= 2.6842 (17)-2.8718 (17) Å, mean 2.776 (2) Å] are associated with the polarized ammonium N-H donors and nitroso O-atom acceptors, which sustain invariant motifs in the form of nitroso/ammonium dimers. Subtle structural changes within this series of compounds concern the rupture of some weaker interactions, i.e. mutual hydrogen bonds of the carbamoyl groups in (1)-(3) [N...O= 2.910 (2)-2.9909 (18) Å; mean 2.950 (2) Å] and carbamoyl/nitrile hydrogen bonds in (1), (2) and (4) [N...N= 2.936 (2)-3.003 (3) Å, mean 2.977 (2) Å], providing a gradual evolution of the hydrogen-bonding pattern. A hierarchy of the synthons involving three different groups could be applicable to supramolecular synthesis with polyfunctional methanide species, suggesting also a degree of control over layered and interpenetrated hydrogen-bonded networks.

Cardiac wasting in head and neck cancer and in cardiac autopsies from different cancer types: A study in a chemo-naïve setting.

Cardiac wasting is a detrimental consequence of cancer that has been traditionally ignored and often misinterpreted as an iatrogenic effect. We conducted a retrospective study on 42 chemo-naive patients affected by locally advanced head and neck cancer (HNC). Based on unintentional weight loss, patients were divided into cachectic and non-cachectic. Left ventricular mass (LVM), LV wall thickness (LVWT), interventricular septal (IVS) thickness, left ventricular internal diameter diastolic (LVIDd), left ventricular internal diameter systolic (LVIDs), internal ventricular septum diastolic (IVSd), left ventricular posterior wall thickness diastolic (LVPWd) and LV ejection fraction (LVEF) were analysed by echocardiography. In parallel, we retrospectively analysed 28 cardiac autoptic specimens of patients who either died of cancer before chemotherapy or with a diagnosis of cancer at autopsy. Presence or absence of myocardial fibrosis at microscopic observation was used for sample stratification. Conventional histology was performed. Cachectic and non-cachectic patients had a significantly different value of LVWT and IVS thickness and LVPWd. LVWT was 9.08±1.57 versus 10.35±1.41mm (P=0.011) in cachectic and non-cachectic patients, IVS was 10.00mm (8.50-11.00) versus 11.00mm (10.00-12.00) (P=0.035), and LVPWd was 9.0 (8.5-10.0) and 10.00mm (9.5-11.0) (P=0.019) in cachectic and non-cachectic patients. LVM adjusted for body surface area or height squared did not differ between the two populations. Similarly, LVEF did not show any significant decline. At multivariate logistic regression analysis for some independent predictors of weight loss, only LVWT maintained significant difference between cachectic and non-cachectic patients (P=0.035, OR=0.240; P=0.019). The secondary analysis on autoptic specimens showed no significant change in heart weight, whereas LVWT declined from 9.50 (7.25-11.00) to 7.50mm (6.00-9.00) in cardiac specimens with myocardial fibrosis (P=0.043). These data were confirmed in multivariate logistic regression analysis (P=0.041, OR=0.502). Histopathological analysis confirmed severe atrophy of cardiomyocytes, fibrosis and oedema as compared with controls. Subtle changes in heart structure and function occur early in HNC patients. These can be detected with routine echocardiography and may help to select appropriate cancer treatment regimens for these patients. Histopathological analysis provided conclusive evidence that atrophy of cardiomyocytes, oedema and fibrosis occur during cancer progression and may precede the onset of overt cardiac pathology. To our knowledge, this is the first clinical study that establishes a direct relationship between tumour progression and cardiac remodelling in HNCs and the first pathological study conducted on human cardiac autopsies from selected chemo-naïve cancer patients.

From spin liquid to magnetic ordering in the anisotropic kagome Y-kapellasite Y3Cu9(OH)19Cl8 : A single-crystal study

Y${}_{3}$Cu${}_{9}$(OH)${}_{19}$Cl${}_{8}$, also known as Y-kapellasite, realizes an original anisotropic frustrated kagome model. Here, the authors study large phase-pure single crystals, obtained via an external gradient method, by susceptibility, specific heat, thermal expansion, neutron scattering, and local $\ensuremath{\mu}$SR and NMR techniques. These find subtle structural changes along with long-range magnetic ordering (1/3,1/3). Large quantum fluctuations reduce the Cu${}^{2+}$ moments, likely as a result of the proximity to a phase boundary in the rich magnetic phase diagram of the model.

Slow conformational changes in the rigid and highly stable chymotrypsin inhibitor 2.

Slow conformational changes are often directly linked to protein function. It is however less clear how such processes may perturb the overall folding stability of a protein. We previously found that the stabilizing double mutant L49I/I57V in the small protein chymotrypsin inhibitor 2 from barley led to distributed increased nanosecond and faster dynamics. Here we asked what effects the L49I and I57V substitutions, either individually or together, have on the slow conformational dynamics of CI2. We used 15 N CPMG spin relaxation dispersion experiments to measure the kinetics, thermodynamics and structural changes associated with slow conformational change in CI2. These changes result in an excited state that is populated to 4.3% at 1 °C. As the temperature is increased the population of the excited state decreases. Structural changes in the excited state are associated with residues that interact with water molecules that have well defined positions and are found at these positions in all crystal structures of CI2. The substitutions in CI2 have only little effect on the structure of the excited state whereas the stability of the excited state to some extent follows the stability of the main state. The minor state is thus most populated for the most stable CI2 variant and least populated for the least stable variant. We hypothesize that the interactions between the substituted residues and the well-ordered water molecules links subtle structural changes around the substituted residues to the region in the protein that experience slow conformational changes. This article is protected by copyright. All rights reserved.

Probing local changes to α-helical structures with 2D IR spectroscopy and isotope labeling

α-Helical secondary structures impart specific mechanical and physiochemical properties to peptides and proteins, enabling them to perform a vast array of molecular tasks ranging from membrane insertion to molecular allostery. Loss of α-helical content in specific regions can inhibit native protein function or induce new, potentially toxic, biological activities. Thus, identifying specific residues that exhibit loss or gain of helicity is critical for understanding the molecular basis of function. Two-dimensional infrared (2D IR) spectroscopy coupled with isotope labeling is capable of capturing detailed structural changes in polypeptides. Yet, questions remain regarding the inherent sensitivity of isotope-labeled modes to local changes in α-helicity, such as terminal fraying; the origin of spectral shifts (hydrogen-bonding versus vibrational coupling); and the ability to definitively detect coupled isotopic signals in the presence of overlapping side chains. Here, we address each of these points individually by characterizing a short, model α-helix (DPAEAAKAAAGR-NH2) with 2D IR and isotope labeling. These results demonstrate that pairs of 13C18O probes placed three residues apart can detect subtle structural changes and variations along the length of the model peptide as the α-helicity is systematically tuned. Comparison of singly and doubly labeled peptides affirm that frequency shifts arise primarily from hydrogen-bonding, while vibrational coupling between paired isotopes leads to increased peak areas that can be clearly differentiated from underlying side-chain modes or uncoupled isotope labels not participating in helical structures. These results demonstrate that 2D IR in tandem with i,i+3 isotope-labeling schemes can capture residue-specific molecular interactions within a single turn of an α-helix.

Peptide-binding specificity prediction using fine-tuned protein structure prediction networks

Peptide-binding proteins play key roles in biology, and predicting their binding specificity is a long-standing challenge. While considerable protein structural information is available, the most successful current methods use sequence information alone, in part because it has been a challenge to model the subtle structural changes accompanying sequence substitutions. Protein structure prediction networks such as AlphaFold model sequence-structure relationships very accurately, and we reasoned that if it were possible to specifically train such networks on binding data, more generalizable models could be created. We show that placing a classifier on top of the AlphaFold network and fine-tuning the combined network parameters for both classification and structure prediction accuracy leads to a model with strong generalizable performance on a wide range of Class I and Class II peptide-MHC interactions that approaches the overall performance of the state-of-the-art NetMHCpan sequence-based method. The peptide-MHC optimized model shows excellent performance in distinguishing binding and non-binding peptides to SH3 and PDZ domains. This ability to generalize well beyond the training set far exceeds that of sequence-only models and should be particularly powerful for systems where less experimental data are available.

Selective Hydrolysis of Nonactivated Aryl Esters at pH 7 through Cooperative Catalysis.

Most reported artificial esterases only hydrolyze highly activated substrates. We here report synthetic catalysts that hydrolyze nonactivated aryl esters at pH 7, via cooperative action of a thiourea group that mimics the oxyanion hole of a serine protease and a nearby nucleophilic/basic pyridyl group. The molecularly imprinted active site distinguishes subtle structural changes in the substrate, including elongation of the acyl chain by two carbons or shift of a remote methyl group by one carbon.