tailieunhanh - Báo cáo khoa học: Importance of tyrosine residues of Bacillus stearothermophilus serine hydroxymethyltransferase in cofactor binding and L-allo-Thr cleavage Crystal structure and biochemical studies

Serine hydroxymethyltransferase (SHMT) fromBacillus stearothermophilus (bsSHMT) is a pyridoxal 5¢-phosphate-dependent enzyme that catalyses the conversion of l-serine and tetrahydrofolate to glycine and 5,10-methylene tetrahydrofolate. In addition, the enzyme catalyses the tetrahydrofolate-independent cleavage of 3-hydroxy amino acids and transamination. | ễFEBS Journal Importance of tyrosine residues of Bacillus stearothermophilus serine hydroxymethyltransferase in cofactor binding and L-allo-Thr cleavage Crystal structure and biochemical studies B. S. Bhavani1 V. Rajaram2 Shveta Bisht2 Purnima Kaul1 V. Prakash1 M. R. N. Murthy2 N. Appaji Rao3 and H. S. Savithri3 1 Protein Chemistry and Technology CentralFood TechnologicalResearch Institute Mysore India 2 Molecular Biophysics Unit Indian Institute of Science Bangalore India 3 Department of Biochemistry Indian Institute of Science Bangalore India Keywords crystal structure proton abstraction pyridoxal5 -phosphate-dependent enzymes serine hydroxymethyltransferase tetrahydrofolate-independent cleavage Correspondence H. S. Savithri Department of Biochemistry Indian Institute of Science Bangalore-560 012 India Fax 91 80 2360 0814 Tel 91 80 2293 2310 E-mail bchss@ These authors contributed equally to this work Received 8 May 2008 revised 4 July 2008 accepted 18 July 2008 doi Serine hydroxymethyltransferase SHMT from Bacillus stearothermophilus bsSHMT is a pyridoxal 5 -phosphate-dependent enzyme that catalyses the conversion of L-serine and tetrahydrofolate to glycine and 5 10-methylene tetrahydrofolate. In addition the enzyme catalyses the tetrahydrofolate-independent cleavage of 3-hydroxy amino acids and transamination. In this article we have examined the mechanism of the tetrahydrofolate-independent cleavage of 3-hydroxy amino acids by SHMT. The three-dimensional structure and biochemical properties of Y51F and Y61A bsSHMTs and their complexes with substrates especially L-allo-Thr show that the cleavage of 3-hydroxy amino acids could proceed via Ca proton abstraction rather than hydroxyl proton removal. Both mutations result in a complete loss of tetrahydrofolate-dependent and tetrahydrofolate-independent activities. The mutation of Y51 to F strongly affects the binding of pyridoxal 5 -phosphate possibly as a .