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Publication Abstract from PubMed

Cellulolytic clostridia use a highly efficient cellulosome system to degrade polysaccharides. To regulate genes encoding enzymes of the multi-enzyme cellulosome complex, certain clostridia contain alternative sigma I (sigma(I) ) factors that have cognate membrane associated anti-sigma(I) factors (RsgIs) which act as polysaccharide sensors. In this work, we analyzed the structure-function relationship of the extracellular sensory elements of Clostridium (Ruminiclostridium) thermocellum and Clostridium clariflavum (RsgI3 and RsgI4, respectively). These elements were selected for comparison as each comprised two tandem PA14-superfamily motifs. The X-ray structures of the PA14 modular dyads from the two bactrerial species were determined, both of which showed a high degree of structural and sequence similarity, although their binding preferences differed. Bioinformatic approaches indicated that the DNA sequence of promoter of sigI/rsgI operons represents a strong signature which helps differentiate binding specificity of the structurally similar modules. The sigma(I4) -dependent C. clariflavum promoter sequence correlates with binding of RsgI4_PA14 to xylan and was identified in genes encoding xylanases, whereas the sigma(I3) -dependent C. thermocellum promoter sequence correlates with RsgI3_PA14 binding to pectin and regulates pectin degradation-related genes. Structural similarity between clostridial PA14 dyads to PA14-containing proteins in yeast helped identify another crucial signature element: the Calcium Binding Loop 2 (CBL2), which governs binding specificity. Variations in the five amino acids that constitute this loop distinguishes the pectin versus xylan specificities. We propose that the first module (PA14(A) ) is dominant in directing the binding to the ligand in both bacteria. The two X-ray structures of the different PA14 dyads represent the first reported structures of tandem PA14 modules. This article is protected by copyright. All rights reserved.

Distinctive ligand-binding specificities of tandem PA14 biomass-sensory elements from Clostridium thermocellum and Clostridium clariflavum.,Rozman Grinberg I, Yaniv O, Ortiz de Ora L, Munoz-Gutierrez I, Hershko A, Livnah O, Bayer EA, Borovok I, Frolow F, Lamed R, Voronov-Goldman M Proteins. 2019 Jun 4. doi: 10.1002/prot.25753. PMID:31162722^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.