Crystal Structure of MltA from Escherichia coli Reveals a Unique Lytic Transglycosylase Fold

Abstract

Lytic transglycosylases are bacterial enzymes involved in the maintenance and growth of the bacterial cell-wall peptidoglycan. They cleave the b-(1,4)-glycosidic bonds in peptidoglycan forming non-reducing 1,6-anhydro-muropeptides. The crystal structure of the lytic transglycosylase MltA from Escherichia coli without a membrane anchor was solved at 2.0 A ˚ resolution. The enzyme has a fold completely different from those of the other known lytic transglycosylases. It contains two domains, the largest of which has a double-psi b-barrel fold, similar to that of endoglucanase V from Humicola insolens. The smaller domain also has a b-barrel fold topology, which is weakly related to that of the RNA-binding domain of ribosomal proteins L25 and TL5. A large groove separates the two domains, which can accommodate a glycan strand, as shown by molecular modelling. Several conserved residues, one of which is in a position equivalent to that of the catalytic acid of the H. insolens endoglucanase, flank this putative substrate-binding groove. Mutation of this residue, Asp308, abolished all activity of the enzyme, supporting the direct participation of this residue in catalysis.

Identification of the bacterial protein FtsX as a unique target of chemokine-mediated antimicrobial activity against Bacillus anthracis

“…BAS0651 encodes a conserved hypothetical protein; BLASTp analysis of the predicted amino acid sequence identified two conserved domains: a "3D" domain containing three conserved aspartate residues and shown to be part of the catalytic domain of a lytic murein transglycosylase (19), and a structural maintenance of chromosomes (SMC) domain involved in organizing and segregating chromosomes for partition (20). In common with BAS0651, B. anthracis lytE, the third gene identified as being involved in susceptibility to CXCL10, is also predicted to contain a SMC domain and the gene's product, LytE, has been shown to contribute to cell wall lytic activity in B. subtilis (21).…”

Crystal structure and activity of Bacillus subtilis YoaJ (EXLX1), a bacterial expansin that promotes root colonization

“…This may account for the lack of lytic activity in EXLX1 and in plant expansins (5,34). Thus, the structural similarity between expansin and MltA, first noted by van Straaten et al (20), does not mean similar catalytic activity. The D2 domain could potentially increase substrate binding, but its distance from the potential lytic site means it is unlikely to stabilize a LT reaction.…”

Peptidoglycan Hydrolases of Escherichia coli

“…It revealed two domains separated by a large groove (Fig. 3b), which can accommodate a six-residue-long glycan chain and which has a centrally located aspartic acid residue conserved in all known MltAs (206,289). This first structure of a member of LT family 2 showed a fold different from those of the other known LTs.…”

“…The crystal structure of a functional soluble form of MltA lacking its membrane anchor was determined at a 2.0-Å resolution (289). It revealed two domains separated by a large groove (Fig.…”