Background: RpfB is a key factor in resuscitation from dormancy of Mycobacterium tuberculosis. This protein is a cell-wall glycosidase, which cleaves cell-wall peptidoglycan. RpfB is structurally complex and is composed of three types of domains, including a catalytic, a G5 and three DUF348 domains. Structural information is currently limited to a portion of the protein including only the catalytic and G5 domains. To gain insights into the structure and function of all domains we have undertaken structural investigations on a large protein fragment containing all three types of domains that constitute RpfB (RpfB3D).
Methods: The structural features of RpfB3D have been investigated combining x-ray crystallography and biophysical studies.
Results and conclusions: The crystal structure of RpfB3D provides the first structural characterization of a DUF348 domain and revealed an unexpected structural relationship with ubiquitin. The crystal structure also provides specific structural features of these domains explaining their frequent association with G5 domains.
General significance: Results provided novel insights into the mechanism of peptidoglycan degradation necessary to the resuscitation of M. tuberculosis. Features of the DUF348 domain add structural data to a large set of proteins embedding this domain. Based on its structural similarity to ubiquitin and frequent association to the G5 domain, we propose to name this domain as G5-linked-Ubiquitin-like domain, UBLG5.
Keywords: Cell wall; Crystal structure; Peptidoglycan; Tuberculosis.
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