# Structural Insights into MltC from Acinetobacter baumannii: Conservation of the Catalytic Residue and Flexibility in Substrate Recognition

## TL;DR

This paper reveals structural details of MltC from Acinetobacter baumannii, showing how it recognizes substrates and cleaves glycosidic bonds.

## Contribution

The study identifies conserved catalytic and flexible substrate-binding residues in MltC, offering new structural insights into its function.

## Key findings

- The catalytic residue E224 in AbMltC is conserved and directly involved in glycosidic bond cleavage.
- Residue R234 in AbMltC shows multiple conformations, indicating structural flexibility in substrate recognition.
- The findings support the hypothesis that R234 functions as a molecular ratchet for processive cleavage.

## Abstract

Lytic transglycosylases (LTs) are key enzymes involved in bacterial peptidoglycan remodeling. Here, we present the crystal structure of MltC from Acinetobacter baumannii (AbMltC), representing the second reported MltC structure after that of Escherichia coli (EcMltC). The AbMltC structure reveals a conserved catalytic residue, E224, equivalent to E217 of EcMltC, which directly participates in glycosidic bond cleavage. Notably, the substrate-binding residue R234, corresponding to R227 of EcMltC, is conserved in sequence but exhibits multiple conformations in AbMltC. This conformational heterogeneity suggests structural flexibility in substrate recognition and provides the structural insights consistent with prior hypothesis that R234 (R227 in EcMltC) functions as a molecular ratchet, facilitating processive cleavage.