Alternative catalytic residues in the active site of Esco acetyltransferases.

Cohesin is a protein complex whose core subunits, Smc1, Smc3, Scc1, and SA1/SA2 form a ring-like structure encircling the DNA. Cohesins play a key role in the expression, repair, and segregation of eukaryotic genomes. Following a catalytic mechanism that is insufficiently understood, Esco1 and Esco2 acetyltransferases acetylate the cohesin subunit Smc3, thereby inducing stabilization of cohesin on DNA. As a prerequisite for structure-guided investigation of enzymatic activity, we determine here the crystal structure of the mouse Esco2/CoA complex at 1.8 Šresolution. We reconstitute cohesin as tri- or tetrameric assemblies and use those as physiologically-relevant substrates for enzymatic assays in vitro. Furthermore, we employ cell-based complementation studies in mouse embryonic fibroblast deficient for Esco1 and Esco2, as a means to identify catalytically-important residues in vivo. These analyses demonstrate that D567/S566 and E491/S527, located on opposite sides of the murine Esco2 active site cleft, are critical for catalysis. Our experiments support a catalytic mechanism of acetylation where residues D567 and E491 are general bases that deprotonate the ε-amino group of lysine substrate, also involving two nearby serine residues - S566 and S527- that possess a proton relay function.

Additive effect of MTHFR and GRIN1 genetic polymorphisms on the risk of schizophrenia.

Schizophrenia is a complex disorder with polygenic inheritance. The MTHFR gene (OMIM: 607093) plays an important role in the folate metabolism. It has been suggested that C677T (rs1801133) and A1298C (rs1801131) genetic polymorphisms in the MTHFR gene lead to the decreased activity of the methylenetetrahydrofolate reductase enzyme which may have significant effect on developing schizophrenia. We used a case-control study to establish the possible association between the C677T and the A1298C polymorphisms and susceptibility to schizophrenia in an Iranian population. The genotypes of the polymorphisms were determined using PCR-RFLP. The data were analyzed by logistic regression model. Data analysis revealed that the combination genotypes of 677CT/1298AA, 677CC/1298CC, 677TT/1298AA, 677CT/1298AC and 677CT/1298CC increase the risk of schizophrenia. In order to evaluate the effect of combined genotypes of the three mentioned polymorphic loci, the frequencies of the compound genotypes were compared between control and patient groups (Table 4). Base on the results, the existence of >4 risk factors showed about 32-fold increased risk for schizophrenia (OR=32.3, 95% CI: 5.52-188, P=<0.001).