PDBsum entry 4z4a

Sugar binding protein

PDB id: 4z4a

Contents

Protein chains

74 a.a.

Ligands

EDO ×16

Waters ×149

References listed in PDB file

Key reference

• Title: Structural analysis of an avr4 effector ortholog offers insight into chitin binding and recognition by the cf-4 receptor.
• Authors: A.C.Kohler, L.H.Chen, N.Hurlburt, A.Salvucci, B.Schwessinger, A.J.Fisher, I.Stergiopoulos.
• Ref.: Plant Cell, 2016, 28, 1945-1965. [DOI no: 10.1105/tpc.15.00893]
• PubMed id: 27401545

Abstract

Chitin is a key component of fungal cell walls and a potent inducer of innate immune responses. Consequently, fungi may secrete chitin-binding lectins, such as the Cf-Avr4 effector protein from the tomato pathogen Cladosporium fulvum, to shield chitin from host-derived chitinases during infection. Homologs of Cf-Avr4 are found throughout Dothideomycetes, and despite their modest primary sequence identity, many are perceived by the cognate tomato immune receptor Cf-4. Here, we determined the x-ray crystal structure of Pf-Avr4 from the tomato pathogen Pseudocercospora fuligena, thus providing a three-dimensional model of an Avr4 effector protein. In addition, we explored structural, biochemical, and functional aspects of Pf-Avr4 and Cf-Avr4 to further define the biology of core effector proteins and outline a conceptual framework for their pleiotropic recognition by single immune receptors. We show that Cf-Avr4 and Pf-Avr4 share functional specificity in binding (GlcNAc)6 and in providing protection against plant- and microbial-derived chitinases, suggesting a broader role beyond deregulation of host immunity. Furthermore, structure-guided site-directed mutagenesis indicated that residues in Pf-Avr4 important for binding chitin do not directly influence recognition by Cf-4 and further suggested that the property of recognition is structurally separated or does not fully overlap with the virulence function of the effector.