Comparative Infectomic Analysis and Molecular Characterization of CglE, the Invasin IbeA Homologous Protein, Which Contributes to the Pathogenesis of Meningitic E. Coli K1 Infection

Hong Cao, Lidan Chen, Jun Yang, Shuji Gong, Hao Zhou, Yong Jiang, Sheng-He Huang

CglE is a putative dihydrolipoamide dehydrogenase (DLDH) that shares significant protein sequence homology (50% identity and 70% similarity) to the IbeA invasin contributing to the pathogenesis of E. coli meningitis. However, the biochemical, biological and pathogenic functions of CglE are unknown. In order to characterize the role of CglE in the pathogenesis of meningitic infections, infectomic, bioinformatics and molecular approaches were used to analyze and predict its structure and function. First, our comparative infectomic studies showed that CglE and IbeA are present in the genetic island GimA as a pair of homologous proteins that are encoded by two different operons, cgl (GimA2) and ibe (GimA4), at different locations. A similar pair of proteins is also present in Silicibacter sp which belongs to the most abundant and ecologically relevant marine bacterial groups. Meningitic E. coli K1 and Silicibacter sp have to survive under harsh environments (cerebrospinal fluid and ocean) with poor nutrition, suggesting that this pair of proteins is important for energy metabolism in the both microbes. Secondly, bioinformatic analysis indicated that CglE is a putative DLDH, which is the E3 component of pyruvate dehydrogenase complex. A FAD-binding domain and homologous flavoprotein regions are present in CglE. DLDH has been identified as virulence factors contributing to the pathogenesis of hepatitis C virus and pneumococcal infections. The sequence of CglE is homology to that of IbeA, an invasion protein of meningitic E. coli, and the surface probability and hydrophilicity are very similar to each other. Thirdly, the expression, purification and biochemical analysis of CglE protein was further carried out to determine whether CglE shares similar functions as IbeA and whether it is a new class of DLDH. The cglE gene was amplified by PCR and subcloned into pET22b(+) then expressed in E. coli BL21(DE3) as a fusion protein with His6 tag at its C-terminus induced by IPTG. CglE fusion protein was purified. Like IbeA, CglE is able to bind to an IbeA-binding protein, vimentin. In further studies, we will examine whether CglE is a new class of DLDH and how it contributes to the pathogenesis of meningitic infections.

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