Evidence for Pentapeptide-Dependent and Independent CheB Methylesterases

• Main Authors: Félix Velando, José A. Gavira, Miriam Rico-Jiménez, Miguel A. Matilla, Tino Krell
• Format: Article
• Language: English
• Published: MDPI AG 2020-11-01
• Series: International Journal of Molecular Sciences
• Subjects: bacterial signal transduction; chemosensory pathways; chemoreceptor; X-ray structure; C-terminal pentapeptide; CheB
• Online Access: https://www.mdpi.com/1422-0067/21/22/8459
• ISSN: 1661-6596; 1422-0067

Many bacteria possess multiple chemosensory pathways that are composed of homologous signaling proteins. These pathways appear to be functionally insulated from each other, but little information is available on the corresponding molecular basis. We report here a novel mechanism that contributes to pathway insulation. We show that, of the four CheB paralogs of <i>Pseudomonas aeruginosa</i> PAO1, only CheB₂ recognizes a pentapeptide at the C-terminal extension of the McpB (Aer2) chemoreceptor (<i>K</i>_D = 93 µM). McpB is the sole chemoreceptor that stimulates the Che2 pathway, and CheB₂ is the methylesterase of this pathway. <i>Pectobacterium atrosepticum</i> SCRI1043 has a single CheB, CheB_Pec, and 19 of its 36 chemoreceptors contain a C-terminal pentapeptide. The deletion of <i>cheB_Pec</i> abolished chemotaxis, but, surprisingly, none of the pentapeptides bound to CheB_Pec. To determine the corresponding structural basis, we solved the 3D structure of CheB_Pec. Its structure aligned well with that of the pentapeptide-dependent enzyme from <i>Salmonella enterica</i>. However, no electron density was observed in the CheB_Pec region corresponding to the pentapeptide-binding site in the <i>Escherichia coli</i> CheB. We hypothesize that this structural disorder is associated with the failure to bind pentapeptides. Combined data show that CheB methylesterases can be divided into pentapeptide-dependent and independent enzymes.