Journal Article

Calixarene-mediated assembly of a small antifungal protein

Rennie, Martin L., Alex, Jimi M., Dorottya, Hajdu, Lehoczki, Gábor, Batta, Gyula, Crowley, Peter B., Engilberge, Sylvain, Fizil, Ádám

2019

Overview

Synthetic macrocycles such as calixarenes and cucurbiturils are increasingly applied as mediators of protein assembly and crystallization. The macrocycle can facilitate assembly by providing a surface on which two or more proteins bind simultaneously. This work explores the capacity of the sulfonato-calix[ n ]arene (sclx n ) series to effect crystallization of PAF, a small, cationic antifungal protein. Co-crystallization with sclx 4 , sclx 6 or sclx 8 led to high-resolution crystal structures. In the absence of sclx n , diffraction-quality crystals of PAF were not obtained. Interestingly, all three sclx n were bound to a similar patch on PAF. The largest and most flexible variant, sclx 8 , yielded a dimer of PAF. Complex formation was evident in solution via NMR and ITC experiments, showing more pronounced effects with increasing macrocycle size. In agreement with the crystal structure, the ITC data suggested that sclx 8 acts as a bidentate ligand. The contributions of calixarene size/conformation to protein recognition and assembly are discussed. Finally, it is suggested that the conserved binding site for anionic calixarenes implicates this region of PAF in membrane binding, which is a prerequisite for antifungal activity.

• Publisher: International Union of Crystallography
• Subject: Antifungal agents / antifungal proteins / Assembly / Binding sites / calixarene / Calixarenes / Complex formation / conformation selection / Crystal structure / Crystallization / Dimers / Fungicides / Ions / molecular glue / NMR / Nuclear magnetic resonance / nucleating agent / polyethylene glycol / Protein binding / Proteins / Research Papers / supramolecular chemistry / Surface active agents