MalY of Escherichia coli is an enzyme with the activity of a beta C-S lyase (cystathionase)

Abstract

The Escherichia coli maltose system consists of a number of genes whose products are involved in the uptake and metabolism of maltose and maltodextrins. MalT is the central positive gene activator of the regulon and is, together with the cyclic AMP-catabolite gene activator protein system, necessary for the expression of the maltose genes. Expression of malY, a MalT-independent gene, leads to the repression of all MalT-dependent genes. We have purified MalY to homogeneity and found it to be a pyridoxal-5-phosphate-containing enzyme with the enzymatic activity of a ␤C-S lyase (cystathionase). MalY is a monomeric protein of 42,000 to 44,000 Da. Strains expressing MalY constitutively abolish the methionine requirement of metC mutants. The enzymatic activity of MetC, the cleavage of cystathionine to homocysteine, ammonia, and pyruvate, can be catalyzed by MalY. However, the cystathionase activity is not required for the function of MalY in repressing the maltose system. By site-directed mutagenesis, we changed the conserved lysine residue at the pyridoxal phosphate binding site (position 233) of MalY to isoleucine. This abolished ␤C-S lyase activity but not the ability of the protein to repress the maltose system. Also, the overexpression of plasmid-encoded metC did not affect mal gene expression, nor did the deduced amino acid sequence of MetC show homology to that of MalY.The maltose regulon of Escherichia coli consists of two sets of genes which encode proteins involved in the uptake and metabolism of maltose and maltodextrins (␣1,4-linked D-glucose polymers) (29). Expression of the maltose genes is dependent on the presence of the inducer, maltotriose, bound to the positive regulator, MalT (23). Mutants lacking MalT function do not express any mal genes and are phenotypically Mal Ϫ , whereas malT(Con) mutations render mal gene expression independent of (or less dependent on) the inducer, maltotriose (10, 11). The expression of malT, as well as of some of the mal genes, is dependent on activation by the cyclic AMP-catabolite gene activator protein complex (9). Several observations demonstrate that the regulation of the maltose system is not as straightforward as implied above. First, there is the phenomenon of internal induction (12). Second, MalK, the ATP-consuming subunit of the maltose transport system, acts phenotypically as a repressor of the system, affecting the function of MalT (6,18,19,26). The third regulatory circuit affecting mal gene expression is derived from the malI malX malY gene cluster. malI was discovered as a mutation which strongly reduced the high and constitutive expression of a malK-lacZ fusion (14). Molecular analysis of malI (25) and its adjacent genes revealed that malI encodes a typical repressor protein, analogous to LacI and GalR, which prevents the expression of the adjacent and divergently oriented malX malY operon. The gene product of malX is a protein homologous to the enzyme II Glc of the phosphotransferase system. malY encodes a protein with sequence homology, including the ch...

Production of hydrogen sulfide by two enzymes associated with biosynthesis of homocysteine and lanthionine in Fusobacterium nucleatum subsp. nucleatum ATCC 25586

“…Like the Cdl protein, Fn1220 showed no significant homology with bC-S lyase, which catalyses the a,belimination of L-cysteine to produce H 2 S, pyruvate and ammonia. Instead, a database analysis demonstrated that the amino acid sequence of Fn0625 was 29-40 % identical with the bC-S lyase proteins encoded by malY in E. coli (Zdych et al, 1995), ytjE in Lactococcus lactis (MartinezCuesta et al, 2006;Sperandio et al, 2005), hly in Treponema denticola (Chu et al, 1995) and lcd in streptococcal species Yoshida et al, 2003Yoshida et al, , 2008. To identify the Fn0625 and Fn1220 proteins in the crude enzyme extracts of strain ATCC 25586, the recombinant proteins were purified (Fig.…”

The N Terminus of the Escherichia coli Transcription Activator MalT Is the Domain of Interaction with MalY

“…MalY is an enzyme with cystathionase activity. This activity is not required for repression; a mutant lacking the enzymatic activity still shows repressor activity (44). On the other hand, mutants can be isolated that exhibit normal cystathionase activity but are defective in their repressor activity (10).…”

Bacterial methionine biosynthesis

“…Of these enzymes, only AecD from C. glutamicum acts physiologically as a cystathionine b-lyase (Ruckert et al, 2003). PatB from B. subtilis (Auger et al, 2005) and MalY from E. coli (Zdych et al, 1995) can catalyse cystathionine b-elimination poorly, while their native activities and physiological roles are unknown.…”