4k39
Native anSMEcpe with bound AdoMet and Cp18Cys peptide
Structural highlights
FunctionANSME_CLOP1 Involved in 'Cys-type' sulfatase maturation under anaerobic conditions. Catalyzes the post-translational modification of cysteine ('Cys-51' in the arylsulfatase CPF_0221) into 3-oxoalanine (also known as C(alpha)-formylglycine (FGly)), by a free radical chemical mechanism initiated via the reductive cleavage of S-adenosyl-L-methionine (SAM). Is also able to oxidize a serine residue in a synthetic substrate to FGly in vitro, and in a serine variant of a Cys-type sulfatase in vivo, but this activity is not physiological.[1] [2] [3] Publication Abstract from PubMedArylsulfatases require a maturating enzyme to perform a co- or posttranslational modification to form a catalytically essential formylglycine (FGly) residue. In organisms that live aerobically, molecular oxygen is used enzymatically to oxidize cysteine to FGly. Under anaerobic conditions, S-adenosylmethionine (AdoMet) radical chemistry is used. Here we present the structures of an anaerobic sulfatase maturating enzyme (anSME), both with and without peptidyl-substrates, at 1.6-1.8 A resolution. We find that anSMEs differ from their aerobic counterparts in using backbone-based hydrogen-bonding patterns to interact with their peptidyl-substrates, leading to decreased sequence specificity. These anSME structures from Clostridium perfringens are also the first of an AdoMet radical enzyme that performs dehydrogenase chemistry. Together with accompanying mutagenesis data, a mechanistic proposal is put forth for how AdoMet radical chemistry is coopted to perform a dehydrogenation reaction. In the oxidation of cysteine or serine to FGly by anSME, we identify D277 and an auxiliary [4Fe-4S] cluster as the likely acceptor of the final proton and electron, respectively. D277 and both auxiliary clusters are housed in a cysteine-rich C-terminal domain, termed SPASM domain, that contains homology to approximately 1,400 other unique AdoMet radical enzymes proposed to use [4Fe-4S] clusters to ligate peptidyl-substrates for subsequent modification. In contrast to this proposal, we find that neither auxiliary cluster in anSME bind substrate, and both are fully ligated by cysteine residues. Instead, our structural data suggest that the placement of these auxiliary clusters creates a conduit for electrons to travel from the buried substrate to the protein surface. X-ray structure of an AdoMet radical activase reveals an anaerobic solution for formylglycine posttranslational modification.,Goldman PJ, Grove TL, Sites LA, McLaughlin MI, Booker SJ, Drennan CL Proc Natl Acad Sci U S A. 2013 May 21;110(21):8519-24. doi:, 10.1073/pnas.1302417110. Epub 2013 May 6. PMID:23650368[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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