A structural model that explains the effects of hyperglycemia on collagenolysis

Investigating biochemical and structural changes of glycated collagen using multimodal multiphoton imaging, Raman spectroscopy, and atomic force microscopy

Advanced glycation end products (AGEs) form extracellular crosslinking with collagenous proteins, which contributes to the development of diabetic complications. In this study, AGEs-related pentosidine (PENT) crosslinks-induced structural and biochemical changes are studied using multimodal multiphoton imaging, Raman spectroscopy and atomic force microscopy (AFM). Decellularized equine pericardium (EP) was glycated with four ribose concentrations ranging between 5 and 200 mM and monitored for up to 30 days. Two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) microscopic imaging probed elastin and collagen fibers, respectively. The glycated EP showed a decrease in the SHG intensities associated with loss of non-centrosymmetry of collagen and an increase of TPEF intensities associated with PENT crosslinks upon glycation. TPEF signals from elastin fibers were unaffected. A three-dimensional reconstruction with SHG + TPEF z-stack images visualized the distribution of collagen and elastin within the EP volume matrix. In addition, Raman spectroscopy (RS) detected changes in collagen-related bands and discriminated glycated from untreated EP. Furthermore, AFM scans showed that the roughness increases and the D-unit structure of fibers remained unchanged during glycation. The PENT crosslinked-induced changes are discussed in the context of previous studies of glutaraldehyde- and genipin-induced crosslinking and collagenase-induced digestion of collagen. We conclude that TPEF, SHG, RS, and AFM are effective, label-free, and non-destructive methods to investigate glycated tissues, differentiate crosslinking processes, and characterize general collagen-associated and disease-related changes, in particular by their RS fingerprints.

Toward Development of a Diabetic Synovium Culture Model

Osteoarthritis (OA) is a degenerative joint disease characterized by articular cartilage degradation and inflammation of synovium, the specialized connective tissue that envelops the diarthrodial joint. Type 2 diabetes mellitus (DM) is often found in OA patients, with nearly double the incidence of arthritis reported in patients with diabetes (52%) than those without it (27%). The correlation between OA and DM has been attributed to similar risk factors, namely increasing age and joint loading due to obesity. However, a potential causative link is not well understood due to comorbidities involved with treating diabetic patients, such as high infection rates and poor healing response caused by hyperglycemia and insulin resistance. The purpose of this study was to investigate the effect of hyperglycemic and insulin culture conditions on synovium properties. It was hypothesized that modeling hyperglycemia-induced insulin resistance in synovium would provide novel insights of OA pathogenesis in DM patients. To simulate DM in the synovial joint, healthy synovium was preconditioned in either euglycemic (EG) or hyperglycemic (HG) glucose concentrations with insulin in order to induce the biological response of the diseased phenotype. Synovium biochemical composition was evaluated to determine ECM remodeling under hyperglycemic culture conditions. Concurrent changes in AKT phosphorylation, a signaling pathway implicated in insulin resistance, were measured along with gene expression data for insulin receptors, glucose transporters, and specific glycolysis markers involved in glucose regulation. Since fluid shear stress arising during joint articulation is a relevant upstream stimulus for fibroblast-like synoviocytes (FLS), the predominant cell type in synovium, FLS mechanotransduction was evaluated via intracellular calcium ([Ca²⁺]_i). Incidence and length of primary cilia, a critical effector of cell mechanosensing, were measured as potential mechanisms to support differences in [Ca²⁺]_i responses. Hyperglycemic culture conditions decreased collagen and GAG content compared to EG groups, while insulin recovered ECM constituents. FLS mechanosensitivity was significantly greater in EG and insulin conditions compared to HG and non-insulin treated groups. Hyperglycemic treatment led to decreased incidence and length of primary cilia and decreased AKT phosphorylation, providing possible links to the mechanosensing response and suggesting a potential correlation between glycemic culture conditions, diabetic insulin resistance, and OA development.

Reduced Muscle Strength Is Associated With Insulin Resistance in Type 2 Diabetes Patients With Osteoarthritis

CONTEXT

Type 2 diabetes is associated with a greater risk for musculoskeletal disorders, yet its impact on joint function remains unclear.

OBJECTIVE

We hypothesized that patients with type 2 diabetes and osteoarthritis would exhibit musculoskeletal impairment, which would associate with insulin resistance and distinct microRNA profiles.

METHODS

Participants of the German Diabetes Study with type 2 diabetes (T2D, n = 39) or normal glucose tolerance (CON, n = 27), both with (+OA) or without osteoarthritis (-OA) underwent intravenous glucose tolerance and hyperinsulinemic-euglycemic clamp tests. Musculoskeletal function was assessed by isometric knee extension strength (KES), grip strength, range of motion (ROM), and balance skills, while neural function was measured by nerve conductance velocity (NCV). Arthritis-related symptoms were quantified using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire, serum arthritis-related microRNA using quantitative polymerase chain reaction.

RESULTS

Insulin sensitivity was lower in T2D+OA vs T2D-OA (4.4 ± 2.0 vs 5.7 ± 3.0 mg* kg-1*min-1) and in CON+OA vs CON-OA (8.1 ± 2.0 vs 12.0 ± 2.6 mg*kg-1,*min-1, both P < .05). In T2D+OA, KES and ROM were 60% and 22% lower than in CON+OA, respectively (both P < .05). Insulin sensitivity correlated positively with KES (r = 0.41, P < .05) among T2D, and negatively with symptom severity in CON and T2D (r = -0.60 and r = -0.46, respectively, P < .05). CON+OA and T2D+OA had inferior balance skills than CON-OA, whereas NCV was comparable in T2D+OA and T2D-OA. Expression of arthritis-related microRNAs was upregulated in T2D compared to CON, but downregulated in CON+OA compared to CON-OA (P < .05), and did not differ between T2D+OA and T2D-OA.

CONCLUSION

Musculoskeletal impairment and osteoarthritis-related symptoms are associated with insulin resistance. Type 2 diabetes can mask changes in arthritis-related microRNA profiles.

Effect of metabolic syndrome on incidence of oral potentially malignant disorder: a prospective cohort study in Taiwan

OBJECTIVES

We aimed to assess the effect of metabolic syndrome (MetS) on incident oral potentially malignant disorder (OPMD).

DESIGN

We conducted a prospective cohort study of the Changhua community-based integrated screening (CHCIS) programme and nationwide oral cancer screening programme during the period between 2005 and 2014.

SETTING

CHCIS, Taiwan.

PARTICIPANTS

We enrolled 17 590 participants aged 30 years and older.

MAIN OUTCOMES AND MEASURES

We assessed the impact of MetS on the outcome measured by incident OPMD.

RESULTS

The incidences of OPMD among subjects with and without MetS were 7.68 ‰ and 5.38 ‰, respectively. After adjusting for confounders, subjects with MetS exhibited a statistically greater risk of developing OPMD compared with those who were free of MetS by 33% (adjusted rate ratio, aRR=1.33, 95% CI 1.14 to 1.55). Individual components of MetS still remained significant, including central obesity (aRR=1.22, 95% CI 1.04 to 1.44), hypertriglyceridaemia (aRR=1.26, 95% CI 1.07 to 1.49) and hyperglycaemia (aRR=1.20, 95% CI 1.02 to 1.41). Central obesity and hypertriglyceridaemia were also statistically associated with a subtype of OPMD, namely, leukoplakia.

CONCLUSION

The temporal influence of MetS on the risk of incident OPMD was noted in our prospective cohort study. Therefore, promoting an MetS prevention and control programme might reduce the occurrence of OPMD and oral cancer.

Tension in fibrils suppresses their enzymatic degradation - A molecular mechanism for 'use it or lose it'

Tissue homeostasis depends on a balance of synthesis and degradation of constituent proteins, with turnover of a given protein potentially regulated by its use. Extracellular matrix (ECM) is predominantly composed of fibrillar collagens that exhibit tension-sensitive degradation, which we review here at different levels of hierarchy. Past experiments and recent proteomics measurements together suggest that mechanical strain stabilizes collagen against enzymatic degradation at the scale of tissues and fibrils whereas isolated collagen molecules exhibit a biphasic behavior that depends on load magnitude. Within a Michaelis-Menten framework, collagenases at constant concentration effectively exhibit a low activity on substrate fibrils when the fibrils are strained by tension. Mechanisms of such mechanosensitive regulation are surveyed together with relevant interactions of collagen fibrils with cells.

The Effects of the Contact Activation System on Hemorrhage

The contact activation system (CAS) exerts effects on coagulation via multiple mechanisms, which modulate both the intrinsic and extrinsic coagulation cascades as well as fibrinolysis and platelet activation. While the effects of the CAS on blood coagulation measured as activated partial thromboplastin time shortening are well documented, genetic mutations that result in deficiencies in the expression of either plasma prekallikrein (PPK) or factor XII (FXII) are not associated with spontaneous bleeding or increased bleeding risk during surgery. Deficiencies in these proteins are often undiagnosed for decades and detected later in life during routine coagulation assays without an apparent clinical phenotype. Increased interest in the CAS as a potentially safe target for antithrombotic therapies has emerged, in large part, from studies on animal models with provoked thrombosis, which have shown that deficiencies in PPK or FXII can reduce thrombus formation without increasing bleeding. Gene targeting and pharmacological studies in healthy animals have confirmed that PPK and FXII blockade does not cause coagulopathies. These findings support the conclusion that CAS is not required for hemostasis. However, while deficiencies in FXII and PPK do not significantly affect bleeding associated with peripheral wounds, recent reports have demonstrated that these proteins can promote hemorrhage in the retina and brain. Intravitreal injection of plasma kallikrein (PKal) induces retinal hemorrhage and intracerebral injection of PKal increases intracranial bleeding. PPK deficiency and PKal inhibition ameliorates hematoma formation following cerebrovascular injury in diabetic animals. Moreover, both PPK and FXII deficiency are protective against intracerebral hemorrhage caused by tissue plasminogen activator-mediated thrombolytic therapy in mice with thrombotic middle cerebral artery occlusion. Thus, while the CAS is not required for hemostasis, its inhibition may provide an opportunity to reduce hemorrhage in the retina and brain. Characterization of the mechanisms and potential clinical implications associated with the effects of the CAS on hemorrhage requires further consideration of the effects of PPK and FXII on hemorrhage beyond their putative effects on coagulation cascades. Here, we review the experimental and clinical evidence on the effects of the CAS on bleeding and hemostatic mechanisms.

Internal strain drives spontaneous periodic buckling in collagen and regulates remodeling

Fibrillar collagen, an essential structural component of the extracellular matrix, is remarkably resistant to proteolysis, requiring specialized matrix metalloproteinases (MMPs) to initiate its remodeling. In the context of native fibrils, remodeling is poorly understood; MMPs have limited access to cleavage sites and are inhibited by tension on the fibril. Here, single-molecule recordings of fluorescently labeled MMPs reveal cleavage-vulnerable binding regions arrayed periodically at ∼1-µm intervals along collagen fibrils. Binding regions remain periodic even as they migrate on the fibril, indicating a collective process of thermally activated and self-healing defect formation. An internal strain relief model involving reversible structural rearrangements quantitatively reproduces the observed spatial patterning and fluctuations of defects and provides a mechanism for tension-dependent stabilization of fibrillar collagen. This work identifies internal-strain-driven defects that may have general and widespread regulatory functions in self-assembled biological filaments.

Identification of an Electrostatic Ruler Motif for Sequence-Specific Binding of Collagenase to Collagen

Sequence-specific cleavage of collagen by mammalian collagenase plays a pivotal role in cell function. Collagenases are matrix metalloproteinases that cleave the peptide bond at a specific position on fibrillar collagen. The collagenase Hemopexin-like (HPX) domain has been proposed to be responsible for substrate recognition, but the mechanism by which collagenases identify the cleavage site on fibrillar collagen is not clearly understood. In this study, Brownian dynamics simulations coupled with atomic-detail and coarse-grained molecular dynamics simulations were performed to dock matrix metalloproteinase-1 (MMP-1) on a collagen IIIα1 triple helical peptide. We find that the HPX domain recognizes the collagen triple helix at a conserved R-X11-R motif C-terminal to the cleavage site to which the HPX domain of collagen is guided electrostatically. The binding of the HPX domain between the two arginine residues is energetically stabilized by hydrophobic contacts with collagen. From the simulations and analysis of the sequences and structural flexibility of collagen and collagenase, a mechanistic scheme by which MMP-1 can recognize and bind collagen for proteolysis is proposed.

Definition of the native and denatured type II collagen binding site for fibronectin using a recombinant collagen system

Interaction of collagen with fibronectin is important for extracellular matrix assembly and regulation of cellular processes. A fibronectin-binding region in collagen was identified using unfolded fragments, but it is not clear if the native protein binds fibronectin with the same primary sequence. A recombinant bacterial collagen is utilized to characterize the sequence requirement for fibronectin binding. Chimeric collagens were generated by inserting the putative fibronectin-binding region from human collagen into the bacterial collagen sequence. Insertion of a sufficient length of human sequence conferred fibronectin affinity. The minimum sequence requirement was identified as a 6-triplet sequence near the unique collagenase cleavage site and was the same in both triple-helix and denatured states. Denaturation of the chimeric collagen increased its affinity for fibronectin, as seen for mammalian collagens. The fibronectin binding recombinant collagen did not contain hydroxyproline, indicating hydroxyproline is not essential for binding. However, its absence may account, in part, for the higher affinity of the native chimeric protein and the lower affinity of the denatured protein compared with type II collagen. Megakaryocytes cultured on chimeric collagen with fibronectin affinity showed improved adhesion and differentiation, suggesting a strategy for generating bioactive materials in biomedical applications.

Synchrotron infrared imaging of advanced glycation endproducts (AGEs) in cardiac tissue from mice fed high glycemic diets

Recent research findings correlate an increased risk for dieases such as diabetes, macular degeneration and cardiovascular disease (CVD) with diets that rapidly raise the blood sugar levels; these diets are known as high glycemic index (GI) diets which include white breads, sodas and sweet deserts. Lower glycemia diets are usually rich in fruits, non-starchy vegetables and whole grain products. The goal of our study was to compare and contrast the effects of a low vs. high glycemic diet using the biochemical composition and microstructure of the heart. The improved spatial resolution and signal-to-noise for SR-FTIR obtained through the coupling of the bright synchrotron infrared photon source to an infrared spectral microscope enabled the molecular-level observation of diet-related changes within unfixed fresh frozen histologic sections of mouse cardiac tissue. High and low glycemic index (GI) diets were started at the age of five-months and continued for one year, with the diets only differing in their starch distribution (high GI diet = 100% amylopectin versus low GI diet = 30% amylopectin/70% amylose). Serial cryosections of cardiac tissue for SR-FTIR imaging alternated with adjacent hematoxylin and eosin (H&E) stained sections allowed not only fine-scale chemical analyses of glycogen and glycolipid accumulation along a vein as well as protein glycation hotspots co-localizing with collagen cold spots but also the tracking of morphological differences occurring in tandem with these chemical changes. As a result of the bright synchrotron infrared photon source coupling, we were able to provide significant molecular evidence for a positive correlation between protein glycation and collagen degradation in our mouse model. Our results bring a new insight not only to the effects of long-term GI dietary practices of the public but also to the molecular and chemical foundation behind the cardiovascular disease pathogenesis commonly seen in diabetic patients.

Structure-based model of allostery predicts coupling between distant sites

Allostery is a phenomenon that couples effector ligand binding at an allosteric site to a structural and/or dynamic change at a distant regulated site. To study an allosteric transition, we vary the size of the allosteric site and its interactions to construct a series of energy landscapes with pronounced minima corresponding to both the effector bound and unbound crystal structures. We use molecular dynamics to sample these landscapes. The degree of perturbation by the effector, modeled by the size of the allosteric site, provides an order parameter for allostery that allows us to determine how microscopic motions give rise to commonly discussed macroscopic mechanisms: (i) induced fit, (ii) population shift, and (iii) entropy driven. These mechanisms involve decreasing structural differences between the effector bound and unbound populations. A metric (ligand-induced cooperativity) can measure how cooperatively a given regulated site responds to effector binding and therefore what kind of allosteric mechanism is involved. We apply the model to three proteins with experimentally characterized transitions: (i) calmodulin-GFP Ca(2+) sensor protein, (ii) maltose binding protein, and (iii) CSL transcription factor. Remarkably, the model is able to reproduce allosteric motion and predict coupling in a manner consistent with experiment.

Hyperglycemia-induced cerebral hematoma expansion is mediated by plasma kallikrein

Hyperglycemia is associated with increased hematoma expansion and worse clinical outcomes following intracerebral hemorrhage. We demonstrate that cerebral hematoma expansion triggered by intracerebral infusion of autologous blood is increased in diabetic rats and mice, and this response is ameliorated by plasma kallikrein (PK) inhibition and deficiency, respectively. Both diabetes and hyperglycemia induced in nondiabetic rats increase hematoma expansion following intracerebral injection of purified PK, a response not observed with bradykinin, plasmin, or tissue plasminogen activator. This response is rapid, prevented by co-injection of the glycoprotein VI (GPVI) agonist convulxin, and mimicked by GPVI inhibition or deficiency. We show that PK binding to collagen and PK-mediated inhibition of collagen-induced platelet aggregation is enhanced by hyperglycemia. Hyperosmotic mannitol also increases hematoma expansion induced by blood and PK, and increases PK-mediated inhibition of platelet aggregation. These findings suggest that hyperglycemia increases cerebral hematoma expansion by PK-mediated osmotic-sensitive inhibition of hemostasis.

Conformational selection and collagenolysis in type III collagen

Matrix metalloproteases (MMPs) cleave native collagen at a single site despite the fact that collagen contains more than one scissile bond that can, in principle, be cleaved. For peptide bond hydrolysis to occur at one specific site, MMPs must (1) localize to a region near the unique scissile bond, (2) bind residues at the catalytic site that form the scissile bond, and (3) hydrolyze the corresponding peptide bond. Prior studies suggest that for some types of collagen, binding of noncatalytic MMP domains to amino acid sequences in the vicinity of the true cleavage site facilitates the localization of collagenases. In the present study, our goal was to determine whether binding to the catalytic site also plays a role in determining MMP specificity. To investigate this, we computed the conformational free energy landscape of Type III collagen at each potential cleavage site. The free energy profiles suggest that although all potential cleavage sites sample unfolded states at relatively low temperatures, the true cleavage site samples structures that are complementary to the catalytic site. By contrast, potential cleavage sites that are not cleaved sample states that are relatively incompatible with the MMP active site. Furthermore, our findings point to a specific role for arginine residues in modulating the structural stability of collagen near the collagenase cleavage site. These data imply that locally unfolded potential cleavage sites in Type III collagen sample distinct unfolded ensembles, and that the region about the true collagenase cleavage site samples states that are most complementary to the MMP active site.

Physical basis of metal-binding specificity in Escherichia coli NikR

In Escherichia coli and other bacteria, nickel uptake is regulated by the transcription factor NikR. Nickel binding at high-affinity sites in E. coli NikR (EcNikR) facilitates EcNikR binding to the nik operon, where it then suppresses transcription of genes encoding the nickel uptake transporter, NikABCDE. A structure of the EcNikR-DNA complex suggests that a second metal-binding site is also present when NikR binds to the nik operon. Moreover, this co-crystal structure raises the question of what metal occupies the second site under physiological conditions: K(+), which is present in the crystal structure, or Ni(2+), which has been proposed to bind to low- as well as high-affinity sites on EcNikR. To determine which ion is preferred at the second metal-binding site and the physical basis for any preference of one ion over another in both the second metal-binding site and the high-affinity sites, we conducted a series of detailed molecular simulations on the EcNikR structure. Simulations that place Ni(2+) at high-affinity sites lead to stable trajectories with realistic ion-ligand distances and geometries, while simulations that place K(+) at these sites lead to conformational changes in the protein that are likely unfavorable for ion binding. By contrast, simulations on the second metal site in the EcNikR-DNA complex lead to stable trajectories with realistic geometries regardless of whether K(+) or Ni(2+) occupies this site. Electrostatic binding free energy calculations, however, suggest that EcNikR binding to DNA is more favorable when the second metal-binding site contains K(+). An analysis of the energetic contributions to the electrostatic binding free energy suggests that, while the interaction between EcNikR and DNA is more favorable when the second site contains Ni(2+), the large desolvation penalty associated with moving Ni(2+) from solution to the relatively buried second site offsets this favorable interaction term. Additional free energy simulations that account for both electrostatic and non-electrostatic effects argue that EcNikR binding to DNA is most favorable when the second site contains a monovalent ion the size of K(+). Taken together, these data suggest that the EcNikR structure is most stable when Ni(2+) occupies high-affinity sites and that EcNikR binding to DNA is more favorable when the second site contains K(+).

Separation of Amadori peptides from their unmodified analogs by ion-pairing RP-HPLC with heptafluorobutyric acid as ion-pair reagent

Glycation is a common class of nonenzymatic posttranslational modifications relevant for several diseases and cell aging in general, such as D: -glucose-derived modifications at the epsilon-amino groups of lysine residues in blood proteins, especially albumin, immunoglobulin, and hemoglobin, for diabetic patients. These Amadori compounds are identified on the peptide level after enzymatic digestion and chromatographic separation by mass spectrometry. Their syntheses usually rely on a global glycation approach. Both areas require the reliable separation of glycated peptides from their unmodified congeners present in different ratios, which is typically not achieved by standard eluent systems in ion-pairing RP-HPLC (IP-RPLC). Here, we compare aqueous acetonitrile and methanol gradients containing either trifluoroacetic acid (TFA) or heptafluorobutyric acid (HFBA) as ion-pairing agents to separate such peptide pairs. TFA-containing eluents resulted in rather low resolutions, and the glycated and unglycated peptides often coeluted. HFBA increased the retention times of the unmodified peptide more than for the glycated peptide thereby improving the separation of all eight studied peptide pairs, even achieving baseline separations for some sequences. Thus the use of HFBA as ion-pair reagent provides a universally applicable eluent system in IP-RPLC to separate glycated peptides from their unmodified counterparts, even at the preparative scale required for synthetic peptides.

Differential unfolding of alpha1 and alpha2 chains in type I collagen and collagenolysis

Collagenolysis plays a central role in many disease processes and a detailed understanding of the mechanism of collagen degradation is of immense interest. While a considerable body of information about collagenolysis exists, the details of the underlying molecular mechanism are unclear. Therefore, to further our understanding of the precise mechanism of collagen degradation, we used molecular dynamics simulations to explore the structure of human type I collagen in the vicinity of the collagenase cleavage site. Since post-translational proline hydroxylation is an important step in the synthesis of collagen chains, we used the DNA sequence for the alpha1 and alpha2 chains of human type I collagen, and the known amino acid sequences for bovine and chicken type I collagen, to infer which prolines are hydroxylated in the vicinity of the collagenase cleavage site. Simulations of type I collagen in this region suggest that partial unfolding of the alpha2 chain is energetically preferred relative to unfolding of alpha1 chains. Localized unfolding of the alpha2 chain leads to the formation of a structure that has disrupted hydrogen bonds N-terminal to the collagenase cleavage site. Our data suggest that this disruption in hydrogen bonding pattern leads to increased chain flexibility, thereby enabling the alpha2 chain to sample different partially unfolded states. Surprisingly, our data also imply that alpha2 chain unfolding is mediated by the non-hydroxylation of a proline residue that is N-terminal to the cleavage site in alpha1 chains. These results suggest that hydroxylation on one chain (alpha1) can affect the structure of another chain (alpha2), and point to a critical role for the non-hydroxylation of proline residues near the collagenase cleavage site.

Do collagenases unwind triple-helical collagen before peptide bond hydrolysis? Reinterpreting experimental observations with mathematical models

It has been postulated that triple-helical collagen is actively unwound by collagenases before peptide bond hydrolysis--a supposition that explains the small catalytic rate constant associated with collagenolysis. We propose an alternate model of collagen degradation that does not require active unwinding by collagenases, but instead suggests that the regions of collagen near the collagenase cleavage site can adopt either a native triple-helical or a partially unfolded conformation. In this model, collagenases preferentially bind to and stabilize partially unfolded conformers before cleaving the scissile bond. Existing experimental observations (which were previously taken to support active unwinding models) are reinterpreted using corroborative evidence from numerical simulations and found to be consistent with this framework. These data support the notion that collagen, like all other biological heteropolymers, undergoes thermal fluctuations that cause it to sample distinct structures in the neighborhood of the native state, and collagenolysis occurs when collagenases recognize the appropriate unwound conformers.

Cell and biomolecular mechanics in silico

Recent developments in computational cell and biomolecular mechanics have provided valuable insights into the mechanical properties of cells, subcellular components and biomolecules, while simultaneously complementing new experimental techniques used for deciphering the structure-function paradigm in living cells. These computational approaches have direct implications in understanding the state of human health and the progress of disease and can therefore aid immensely in the diagnosis and treatment of diseases. We provide an overview of the computational approaches that are currently used in understanding various aspects of cell and bimolecular mechanics. Our emphasis is on state-of-the-art techniques and the progress made in addressing key challenges in biomechanics.

Carbamylation differentially alters type I collagen sensitivity to various collagenases

Carbamylation is a post-translational modification due to nonenzymatic binding of cyanate, a by-product of urea, on free amino groups of proteins. Post-translational modifications are known to induce alterations in structural and functional properties of proteins, thus disturbing protein-protein or cell-protein interactions. We report the impact of carbamylation on type I collagen sensitivity to enzymatic proteolysis. Type I collagen was extracted from rat tail tendons and carbamylated by incubation with 0.1 M potassium cyanate at 37 degrees C for 2, 6 or 24 h. Degradation assays revealed that carbamylated collagen exhibited a greater resistance to collagenases (i.e. bacterial collagenase, matrix metalloproteinase(MMP)-1, MMP-8 and MMP-13), together with an increased sensitivity to MMP-2. Evaluation of collagen triple helix conformation by polarimetry indicated that local destabilizations of triple helix structure related to carbamylation could be responsible for the observed differences in sensitivity. These results confirm the crucial role of triple helix integrity in the degradation of type I collagen by MMPs, and support the deleterious impact of post-translational modifications in vivo by altering the balanced remodeling of collagen within connective tissue.