type	Journal Article
authors	Saito, K.; Kurosawa, M.; Murakoshi, I.
title	Determination of a functional lysine residue of a plant cysteine synthase by site-directed mutagenesis, and the molecular evolutionary implications
journal	FEBS Lett
Activity	2.5.1.47
ui	93345669
year	(1993)
volume	328
number	1-2
pages	111-4.
keywords	Amino Acid Sequence
abstract	Comparison of seven deduced amino acid sequences of cysteine synthase (O-acetyl-L-serine (thiol)-lyase, EC 4.2.99.8) from plants and bacteria disclosed the presence of 12 conserved Lys residues, which can be candidates for a functional binding site for pyridoxal phosphate cofactor. These 12 conserved Lys residues in a cDNA clone encoding spinach cysteine synthase A were replaced with Gly by oligonucleotide- directed in vitro mutagenesis. These Lys-->Gly mutated cDNAs were transferred into Escherichia coli NK3, a cysteine auxotroph lacking both cysteine synthase loci, cysK and cysM. One mutant replaced at Lys- 49 could not complement the cysteine requirement of NK3, whereas other mutants and wild-type clone could. No enzymatic activity of cysteine synthase A was detected either in the cell-free extracts of E. coli NK3 transformed with the Lys-49 mutant. These results indicated that Lys-49 is a functional residue for the catalytic activity of cysteine synthase. This Lys residue is conserved in other evolutionarily related amino acid-metabolizing enzymes catalyzing reactions involving the beta- carbon of amino acids.
last changed	2003/03/17 14:53