A Drosophila pattern recognition receptor contains a peptidoglycan docking groove and unusual L,D-carboxypeptidase activity.
The Drosophila peptidoglycan recognition protein SA (PGRP-SA) is critically involved in sensing bacterial infection and activating the Toll signaling pathway, which induces the expression of specific antimicrobial peptide genes. We have determined the crystal structure of PGRP-SA to 2.2-A resolution and analyzed its peptidoglycan (PG) recognition and signaling activities. We found an extended surface groove in the structure of PGRP-SA, lined with residues that are highly diverse among different PGRPs. Mutational analysis identified it as a PG docking groove required for Toll signaling and showed that residue Ser158 is essential for both PG binding and Toll activation. Contrary to the general belief that PGRP-SA has lost enzyme function and serves primarily for PG sensing, we found that it possesses an intrinsic L,D-carboxypeptidase activity for diaminopimelic acid-type tetrapeptide PG fragments but not lysine-type PG fragments, and that Ser158 and His42 may participate in the hydrolytic activity. As L,D-configured peptide bonds exist only in prokaryotes, this work reveals a rare enzymatic activity in a eukaryotic protein known for sensing bacteria and provides a possible explanation of how PGRP-SA mediates Toll activation specifically in response to lysine-type PG.
Chang
Chung-I
CI
Howard Hughes Medical Institute and Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Pili-Floury
Sébastien
S
Hervé
Mireille
M
Parquet
Claudine
C
Chelliah
Yogarany
Y
Lemaitre
Bruno
B
Mengin-Lecreulx
Dominique
D
Deisenhofer
Johann
J
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002268:Carboxypeptidases / Q000737:chemistry*; D002352:Carrier Proteins / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D003433:Crosses, Genetic; D018360:Crystallography, X-Ray; D004252:DNA Mutational Analysis; D029721:Drosophila Proteins / Q000378:metabolism; D004331:Drosophila melanogaster; D006868:Hydrolysis; D008239:Lysine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010457:Peptidoglycan / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D051193:Toll-Like Receptors / Q000378:metabolism; D014443:Tyrosine / Q000737:chemistry
D002352:Carrier Proteins; D029721:Drosophila Proteins; D010457:Peptidoglycan; D011994:Recombinant Proteins; C068721:Tl protein, Drosophila; D051193:Toll-Like Receptors; C439909:imd protein, Drosophila; C118897:peptidoglycan recognition protein; D014443:Tyrosine; D002268:Carboxypeptidases; D008239:Lysine