Fig. 3.

Structural comparison between PGRP-bound PGN analogs in crystal structures and unbound GMPP₂ in solution. (A) Conformational comparison of GMPP, MPP, TCT, and GMPP₂. GMPP, MPP, and TCT are from crystal structures of complexes with human PGRP-IβC, human PGRP-IαC (16), and Drosophila PGRP-LE (27), respectively; GMPP₂ is from the unliganded NMR structure (17). The structures are superposed through the pyranose ring of NAM (for MPP, GMPP, and GMPP₂) or NAM(1,6-anhydro) (for TCT). (B) Superposition of unbound GMPP₂ onto GMPP in the PGRP-IβC–GMPP complex. GMPP and GMPP₂ are shown in ball-and-stick representations, with carbon atoms in yellow and green, respectively, nitrogen atoms in blue, and oxygen atoms in red. Of the two GMPP units in GMPP₂, the first unit, comprising the NAG₁-NAM₁ disaccharide, is superposed onto GMPP in the complex. The peptide stem of GMPP₂ attached to NAM₁ is buried within PGRP-IβC and is shown in pale green. (C) Alternative superposition of unliganded GMPP₂ onto GMPP bound to PGRP-IβC. In this case, the second GMPP unit of GMPP₂, containing NAG₂-NAM₂, is superposed onto GMPP in the PGRP-IβC–GMPP structure. The peptide stem of GMPP₂ attached to NAM₂, shown in pale green, is buried inside PGRP-IβC. (D) Modeled PGRP-IβC–GMPP₂ structure.