T. Weber et al., Solution structure of PCP, a prototype for the peptidyl carrier domains ofmodular peptide synthetases, STRUCT F D, 8(4), 2000, pp. 407-418
Background: Nonribosomal peptide synthetases (NRPSs) are large modular enzy
mes responsible for the synthesis of a variety of microbial bioactive pepti
des, They consist of modules that each recognise and incorporate one specif
ic amino acid into the peptide product, A module comprises several domains,
which carry out the individual reaction steps. After activation by the ade
nylation domain, the amino acid substrate is covalently tethered to a 4'-ph
osphopantetheinyl cofactor of a peptidyl carrier domain (PCP) that passes t
he substrate to the reaction centres of the consecutive domains.
Results: The solution structure of PCP, a distinct peptidyl carrier protein
derived from the equivalent domain of an NRPS, was solved using NMR techni
ques. PCP is a distorted four-helix bundle with an extended loop between th
e first two helices, its overall fold resembles the topology of acyl carrie
r proteins (ACPs) from Escherichia coli fatty acid synthase and actinorhodi
n polyketide synthase from Streptomyces coelicolor; however, the surface po
larity and the length and relative alignment of the helices are different.
The conserved serine, which is the cofactor-binding site, has the same loca
tion as in the ACPs and is situated within a stretch of seven flexible resi
dues.
Conclusions: The structure of PCP reflects its character as a protein domai
n. The fold is well defined between residues 8 and 82 and the structural co
re of the PCP domain can now be defined as a region spanning 37 amino acids
in both directions from the conserved serine. The flexibility of the post-
translationally modified site might have implications for interactions with
the cooperating proteins or NRPS domains.