Posttranslational conversion of L-serines to D-alanines is vital for optimal production and activity of the lantibiotic lacticin 3147.
As a general rule, ribosomally synthesized polypeptides contain amino acids only in the L-isoform in an order dictated by the coding DNA/RNA. Two of a total of only four examples of L to D conversions in prokaryotic systems occur in posttranslationally modified antimicrobial peptides called lantibiotics. In both examples (lactocin S and lacticin 3147), ribosomally encoded L-serines are enzymatically converted to D-alanines, giving rise to an apparent mistranslation of serine codons to alanine residues. It has been suggested that this conversion results from a two-step reaction initiated by a lantibiotic synthetase converting the gene-encoded L-serine to dehydroalanine (dha). By using lacticin 3147 as a model system, we report the identification of an enzyme, LtnJ, that is responsible for the conversion of dha to D-alanine. Deletion of this enzyme results in the residues remaining as dha intermediates, leading to a dramatic reduction in the antimicrobial activity of the producing strain. The importance of the chirality of the three D-alanines present in lacticin 3147 was confirmed when these residues were systematically substituted by L-alanines. In addition, substitution with L-threonine (ultimately modified to dehydrobutyrine), glycine, or L-valine also resulted in diminished peptide production and/or relative activity, the extent of which depended on the chirality of the newly incorporated amino acid(s).
Cotter
Paul D
PD
Department of Microbiology, University College Cork, Cork, Ireland.
O'Connor
Paula M
PM
Draper
Lorraine A
LA
Lawton
Elaine M
EM
Deegan
Lucy H
LH
Hill
Colin
C
Ross
R Paul
RP
D000409:Alanine / Q000378:metabolism*; D000595:Amino Acid Sequence; D001430:Bacteriocins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003062:Codon / Q000235:genetics; D005998:Glycine / Q000235:genetics; D013294:Lactococcus lactis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D011499:Protein Processing, Post-Translational; D012694:Serine / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013912:Threonine / Q000235:genetics; D014633:Valine / Q000235:genetics
D001430:Bacteriocins; D003062:Codon; C082508:lacticin 481; D013912:Threonine; D012694:Serine; D014633:Valine; D000409:Alanine; D005998:Glycine