5onc | pdb_00005onc
Catabolism of the Cholesterol Side Chain in Mycobacterium tuberculosis is Controlled by a Redox-Sensitive Thiol Switch
Structural highlights
Function[FADA5_MYCTU] Involved in the beta-oxidation of the cholesterol side chain (PubMed:19822655). It is important for utilization of cholesterol as a sole carbon source in vitro and for full virulence in the chronic stage of mouse lung infection (PubMed:19822655). Catalyzes the thiolysis of 3,22-dioxochol-4-en-24-oyl-CoA to yield 3-oxo-4-pregnene-20-carboxyl-CoA (3-OPC-CoA) and acetyl-CoA (PubMed:25482540). Also able to use acetoacetyl-CoA (AcAcCoA) as substrate (PubMed:19822655).[1] [2] Publication Abstract from PubMedMycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a highly successful human pathogen and has infected approximately one-third of the world's population. Multiple drug resistant (MDR) and extensively drug resistant (XDR) TB strains and coinfection with HIV have increased the challenges of successfully treating this disease pandemic. The metabolism of host cholesterol by Mtb is an important factor for both its virulence and pathogenesis. In Mtb, the cholesterol side chain is degraded through multiple cycles of beta-oxidation and FadA5 (Rv3546) catalyzes side chain thiolysis in the first two cycles. Moreover, FadA5 is important during the chronic stage of infection in a mouse model of Mtb infection. Here, we report the redox control of FadA5 catalytic activity that results from reversible disulfide bond formation between Cys59-Cys91 and Cys93-Cys377. Cys93 is the thiolytic nucleophile, and Cys377 is the general acid catalyst for cleavage of the beta-keto-acyl-CoA substrate. The disulfide bond formed between the two catalytic residues Cys93 and Cys377 blocks catalysis. The formation of the disulfide bonds is accompanied by a large domain swap at the FadA5 dimer interface that serves to bring Cys93 and Cys377 in close proximity for disulfide bond formation. The catalytic activity of FadA5 has a midpoint potential of -220 mV, which is close to the Mtb mycothiol potential in the activated macrophage. The redox profile of FadA5 suggests that FadA5 is fully active when Mtb resides in the unactivated macrophage to maximize flux into cholesterol catabolism. Upon activation of the macrophage, the oxidative shift in the mycothiol potential will decrease the thiolytic activity by 50%. Thus, the FadA5 midpoint potential is poised to rapidly restrict cholesterol side chain degradation in response to oxidative stress from the host macrophage environment. Catabolism of the Cholesterol Side Chain in Mycobacterium tuberculosis Is Controlled by a Redox-Sensitive Thiol Switch.,Lu R, Schaefer CM, Nesbitt NM, Kuper J, Kisker C, Sampson NS ACS Infect Dis. 2017 Aug 16. doi: 10.1021/acsinfecdis.7b00072. PMID:28786661[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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