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Crystal structure and biochemical properties of putrescine carbamoyltransferase from Enterococcus faecalis : Assembly, active site, and allosteric regulation
Author(s) -
Shi Dashuang,
Yu Xiaolin,
Zhao Gengxiang,
Ho Jeremy,
Lu Shen,
Allewell Norma M.,
Tuchman Mendel
Publication year - 2012
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.24042
Subject(s) - aspartate carbamoyltransferase , trimer , ornithine carbamoyltransferase , biochemistry , biology , protein subunit , helix (gastropod) , stereochemistry , allosteric regulation , protein structure , agmatine , chemistry , putrescine , gene , enzyme , ornithine , dimer , arginine , amino acid , ecology , organic chemistry , snail
Abstract Putrescine carbamoyltransferase (PTCase) catalyzes the conversion of carbamoylputrescine to putrescine and carbamoyl phosphate (CP), a substrate of carbamate kinase (CK). The crystal structure of PTCase has been determined and refined at 3.2 Å resolution. The trimeric molecular structure of PTCase is similar to other carbamoyltransferases, including the catalytic subunit of aspartate carbamoyltransferase (ATCase) and ornithine carbamoyltransferase (OTCase). However, in contrast to other trimeric carbamoyltransferases, PTCase binds both CP and putrescine with Hill coefficients at saturating concentrations of the other substrate of 1.53 ± 0.03 and 1.80 ± 0.06, respectively. PTCase also has a unique structural feature: a long C ‐terminal helix that interacts with the adjacent subunit to enhance intersubunit interactions in the molecular trimer. The C ‐terminal helix appears to be essential for both formation of the functional trimer and catalytic activity, since truncated PTCase without the C ‐terminal helix aggregates and has only 3% of native catalytic activity. The active sites of PTCase and OTCase are similar, with the exception of the 240′s loop. PTCase lacks the proline‐rich sequence found in knotted carbamoyltransferases and is unknotted. A Blast search of all available genomes indicates that 35 bacteria, most of which are Gram‐positive, have an agcB gene encoding PTCase located near the genes that encode agmatine deiminase and CK, consistent with the catabolic role of PTCase in the agmatine degradation pathway. Sequence comparisons indicate that the C ‐terminal helix identified in this PTCase structure will be found in all other PTCases identified, suggesting that it is the signature feature of the PTCase family of enzymes Proteins 2012; © 2012 Wiley Periodicals, Inc.