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X‐ray structure of MalY from Escherichia coli : a pyridoxal 5′‐phosphate‐dependent enzyme acting as a modulator in mal gene expression
Author(s) -
Clausen Tim,
Schlegel Anja,
Peist Ralf,
Schneider Eva,
Steegborn Clemens,
Chang YuhShin,
Haase Andrea,
Bourenkov Gleb P.,
Bartunik Hans D.,
Boos Winfried
Publication year - 2000
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/19.5.831
Subject(s) - biology , repressor , mutant , biochemistry , pyridoxal phosphate , microbiology and biotechnology , pyridoxal , enzyme , cofactor , gene , gene expression
MalY represents a bifunctional pyridoxal 5′‐phosphate‐dependent enzyme acting as a β‐cystathionase and as a repressor of the maltose regulon. Here we present the crystal structures of wild‐type and A221V mutant protein. Each subunit of the MalY dimer is composed of a large pyridoxal 5′‐phosphate‐binding domain and a small domain similar to aminotransferases. The structural alignment with related enzymes identifies residues that are generally responsible for β‐lyase activity and depicts a unique binding mode of the pyridoxal 5′‐phosphate correlated with a larger, more flexible substrate‐binding pocket. In a screen for MalY mutants with reduced mal repressor properties, mutations occurred in three clusters: I, 83–84; II, 181–189 and III, 215–221, which constitute a clearly distinguished region in the MalY crystal structure far away from the cofactor. The tertiary structure of one of these mutants (A221V) demonstrates that positional rearrangements are indeed restricted to regions I, II and III. Therefore, we propose that a direct protein–protein interaction with MalT, the central transcriptional activator of the maltose system, underlies MalY‐dependent repression of the maltose system.