A single residue substitution accounts for the significant difference in thermostability between two isoforms of human cytosolic creatine kinase

Ancestral contribution of the muscle-specific creatine kinase (CKM) polymorphism rs4884 in the knee osteoarthritis risk: a preliminary study

INTRODUCTION/OBJECTIVES

Articular cartilage and periarticular muscle tissues are strongly affected during knee osteoarthritis (OA). Creatine kinase (CK) is an enzyme expressed in several tissues, but the isoform CK-MM is specific of skeletal muscle, and its serum concentration is used as a biomarker of muscle damage. Genetic variants of the CKM gene have been associated with various pathologies, but to date, there are no reports of association with OA. Due to the rs4884 polymorphism being well represented in the Mexican population, it is used as an ancestry informative marker; thus, the goal of this preliminary report was to evaluate the association of this polymorphism in primary knee OA Mexican patients.

METHOD

Eighty-seven patients with primary knee OA were compared with 107 healthy controls. Serum CK-MM was determined using the dot blot system, and genotyping was performed using the OpenArray system. Logistic regression models were used to assess the association between the rs4884 polymorphism and OA susceptibility adjusting by gender, age, and body mass index.

RESULTS

There were no significant differences in serum CK-MM values between patients and controls. The GG genotype and the G allele had a higher frequency in the control group compared with the OA group (24.3% vs. 12.6%, OR = 0.34, 95% CI = 0.14-0.84, P = 0.019; and 40.2% vs. 28.2%, OR = 0.51, 95% CI = 0.32-0.82, P = 0.005, respectively).

CONCLUSIONS

Our results suggest a protection role of the rs4884 polymorphism against knee OA development; further studies are required to confirm it. Key Points • CK-MM enzyme catalyzes the conversion of creatine and ATP to create phosphocreatine and ADP; this reaction is reversible. • In tissues that consume ATP rapidly, such as skeletal muscle, the phosphocreatine serves as an important energy reservoir. • During knee OA, peripheral muscle tissues of the joint may be affected. • The rs4884 polymorphism of the CKM gene may participate as a protective factor in the development of OA.

Dissimilarity in the Contributions of the N-Terminal Domain Hydrophobic Core to the Structural Stability of Lens β/γ-Crystallins

Vertebrate lens β/γ-crystallins share a conserved tertiary structure consisting of four Greek-key motifs divided into two globular domains. Numerous inherited mutations in β/γ-crystallins have been linked to cataractogenesis. In this research, the folding mechanism underlying cataracts caused by the I21N mutation in βB2 was investigated by comparing the effect of mutagenesis on the structural features and stability of four β/γ-crystallins, βB1, βB2, γC, and γD. Our results showed that the four β/γ-crystallins differ greatly in solubility and stability against various stresses. The I21N mutation greatly impaired βB2 solubility and native structure as well as its stability against denaturation induced by guanidine hydrochloride, heat treatment, and ultraviolet irradiation. However, the deleterious effects were much weaker for mutations at the corresponding sites in βB1, γC, and γD. Molecular dynamics simulations indicated that the introduction of a nonnative hydrogen bond contributed to twisting Greek-key motif I outward, which might direct the misfolding of the I21N mutant of βB2. Meanwhile, partial hydration of the hydrophobic interior of the domain induced by the mutation destabilized βB1, γC, and γD. Our findings highlight the importance of nonnative hydrogen bond formation and hydrophobic core hydration in crystallin misfolding caused by inherited mutations.

Insights into the mechanism of the PIK3CA E545K activating mutation using MD simulations

Phosphoinositide 3-kinase alpha (PI3Kα) is involved in fundamental cellular processes including cell proliferation and differentiation and is frequently mutated in human malignancies. One of the most common mutations is E545K, which results in an amino acid substitution of opposite charge. It has been recently proposed that in this oncogenic charge-reversal mutation, the interactions between the protein catalytic and regulatory subunits are abrogated, resulting in loss of regulation and constitutive PI3Kα activity, which can lead to oncogenesis. To assess the mechanism of the PI3Kα E545K activating mutation, extensive Molecular Dynamics simulations were performed to examine conformational changes differing between the wild type (WT) and mutant proteins as they occur in microsecond simulations. In the E545K mutant PI3Kα, we observe a spontaneous detachment of the nSH2 PI3Kα domain (regulatory subunit, p85α) from the helical domain (catalytic subunit, p110α) causing significant loss of communication between the regulatory and catalytic subunits. We examine the allosteric network of the two proteins and show that a cluster of residues around the mutation is important for delivering communication signals between the catalytic and regulatory subunits. Our results demonstrate the dynamical and structural effects induced by the p110α E545K mutation in atomic level detail and indicate a possible mechanism for the loss of regulation that E545K confers on PI3Kα.

The hydrogen-bond network around Glu160 contributes to the structural stability of chitosanase CsnA from Renibacterium sp. QD1

CsnA, a chitosanase from Renibacterium sp. QD1, has great potential for industrial applications due to its high yield and broad pH stability. In this study, a specific Glu160 in CsnA was identified by sequence alignment, and structural analysis and MD simulation predicted that Glu160 formed a hydrogen-bond network with Lys163 and Thr114. To evaluate the effect of the network, we constructed four mutants, including E160A, E160Q, K163A, and T114A, which partially or completely destroy this network. Characterization of these mutants demonstrated that the disruption of the network significantly decreased the enzyme thermostability. The underlying mechanisms responsible for the change of thermostability analyzed by circular dichroism spectroscopy revealed that the hydrogen-bond network conferred the structural stability of CsnA. Moreover, the length of the side chain of residue at 160 impacted conformational stability of the enzyme. Taken together, the hydrogen-bond network around Glu160 plays important roles in stabilization of CsnA.