Structural analysis of CACHE domain of the McpA chemoreceptor from Leptospira interrogans

Abstract

Leptospira is a genus of spirochete bacteria highly motile that includes pathogenic species responsible to cause leptospirosis disease. Chemotaxis and motility are required for Leptospira infectivity, pathogenesis, and invasion of bacteria into the host. In prokaryotes, the most common chemoreceptors are methyl-accepting chemotaxis proteins that have a role play to detect the chemical signals and move to a favorable environment for its survival. Here, we report the first crystal structure of CACHE domain of the methyl-accepting chemotaxis protein (McpA) of L. interrogans. The structural analysis showed that McpA adopts similar α/β architecture of several other bacteria chemoreceptors. We also found a typical dimerization interface that appears to be functionally crucial for signal transmission and chemotaxis. In addition to McpA structural analyses, we have identified homologous proteins and conservative functional regions using bioinformatics techniques. These results improve our understanding the relationship between chemoreceptor structures and functions of Leptospira species.

Keywords: Bacterial chemoreceptor; CACHE domain; Chemotaxis; Crystal structure; Leptospira interrogans; McpA.

Figure 1.. Bioinformatics prediction of L. interrogans serovar Copenhageni McpA conserved domains, topology and phylogenetic tree.

(A) Predicted McpA topology. TM: transmembrane section; CC: coiled coil. Schematic representation of McpA insertion into leptospiral inner membrane. In blue, the ligand-binding region (Cache domain). In orange, the signal transduction region, comprising the MCPsignal domain and two methylation regions, which form antiparallel alpha-helices embedded in the cytoplasm. The transmembrane sections (TM1 and TM2) flank the ligand-binding domain (LBD), which loops to the periplasmic space. (B). L. interrogans serovar Copenhageni McpA (LIC12921) homologs were searched through PSI-BLAST excluding the Leptospiraceae. The search resulted in 473 proteins from different microorganisms. A Neighbour-joining Phylogenetic Tree without distance corrections was constructed in the MUSCLE webserver. The phylogenetic tree data was edited in the iTOL software. The grey circles correspond to collapsed branches formed by more than one seed protein.

Figure 2.. Overall fold and structural comparison of the McpA with other bacteria chemoreceptors.

(A) Ribbon representation of the McpA-LBD. α-helices and β-strands are represented as coils and arrows, respectively. The chloride ion is represented as a yellow sphere and 1,2-ethanediol is shown with the carbon atoms colored yellow, and oxygen atoms red. On top is represented membrane-distal domain and at the bottom membrane-proximal domain. The α1 in orange, belongs to both domains. The N- and C- terminal are labeled. The topology representation of the secondary structure elements. The a-helices are represented by rods and β-strands by arrows. (B) Cartoon representation of the CACHE_1 domain homodimer. The dimerization interface is formed mainly by hydrophilic residues of both distal and proximal domains.

Figure 3.. Structure-based sequence alignment of LBD-McpA with other bacteria chemoreceptors.

Secondary elements of LBD-McpA are noted above the alignment. Residues in red are higher conserved. Numbers correspond to the LBD-McpA sequence. The green triangles correspond to putative residues in active site from McpA based on comparison with TIpQ chemoreceptor.