4kl7
Crystal structure of the catalytic domain of RpfB from Mycobacterium tuberculosis
Structural highlights
FunctionRPFB_MYCTU Factor that stimulates resuscitation of dormant cells. Has peptidoglycan (PG) hydrolytic activity. Active in the pM concentration range. Has little to no effect on actively-growing cells. PG fragments could either directly activate the resuscitation pathway of dormant bacteria or serve as a substrate for endogenous Rpf, resulting in low molecular weight products with resuscitation activity.[1] [2] [3] [4] Reduces lag phase and enhances the growth of quiescent (1 month-old culture) M.tuberculosis; works best between 8 and 128 pM. Increases the number of bacteria that can be recovered from a 3 month-old culture. Stimulates growth of stationary phase M.bovis (a slowly-growing Mycobacterium) as well as M.smegmatis cells (a fast grower). Binds N,N',N-triacetylchitotriose (tri-NAG). A fragment (residues 194-362) hydrolyzes an artificial lysozyme substrate 4-methylumbelliferyl-beta-D-N,N',N-triacetylchitotrioside (MUF tri-NAG). By itself has little activity on cell wall, in combination with RipA is active against cell wall extracts from a number of Actinobacteria; this activity is inhibited by PBP1A (ponA1). Sequential gene disruption indicates RpfB and RpfE are higher than RpfD and RpfC in functional hierarchy.[5] [6] [7] [8] Publication Abstract from PubMedResuscitation of Mtb is crucial to the etiology of Tuberculosis, because latent tuberculosis is estimated to affect one-third of the world population. The resuscitation-promoting factor RpfB is mainly responsible for Mtb resuscitation from dormancy. Given the impact of latent Tuberculosis, RpfB represents an interesting target for tuberculosis drug discovery. However, no molecular models of substrate binding and catalysis are hitherto available for this enzyme. Here, we identified key interactions involved in substrate binding to RpfB by combining x-ray diffraction studies and computational approaches. The crystal structure of RpfB catalytic domain in complex with N,N',N-triacetyl-chitotriose, as described here, provides the first, to our knowledge, atomic representation of ligand recognition by RpfB and demonstrates that the strongest interactions are established by the N-acetylglucosamine moiety in the central region of the enzyme binding cleft. Molecular dynamics analyses provided information on the dynamic behavior of protein-substrate interactions and on the role played by the solvent in RpfB function. These data combined with sequence conservation analysis suggest that Glu-292 is the sole residue crucial for catalysis, implying that RpfB acts via the formation of an oxocarbenium ion rather than a covalent intermediate. Present data represent a solid base for the design of effective drug inhibitors of RpfB. Moreover, homology models were generated for the catalytic domains of all members of the Mtb Rpf family (RpfA-E). The analysis of these models unveiled analogies and differences among the different members of the Rpf protein family. Carbohydrate Recognition by RpfB from Mycobacterium tuberculosis Unveiled by Crystallographic and Molecular Dynamics Analyses.,Squeglia F, Romano M, Ruggiero A, Vitagliano L, De Simone A, Berisio R Biophys J. 2013 Jun 4;104(11):2530-9. doi: 10.1016/j.bpj.2013.04.040. PMID:23746526[9] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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