Modulation of biliverdin dynamics and spectral properties by Sandercyanin. Issue 31 (13th July 2022)

• Record Type: Journal Article
• Authors: Ghosh, Swagatha; Mondal, Sayan; Yadav, Keerti; Aggarwal, Shantanu; Schaefer, Wayne F.; Narayana, Chandrabhas; Subramanian, Ramaswamy
• Is Part Of: RSC advances. Volume 12:Issue 31(2022)
• Page Start: 20296
• Page End: 20304
• Publication Date: 2022-07-13
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d2ra02880h
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : Biliverdin IX-alpha undergoes rotation around the D-ring pyrrole and displays a broad far-red absorbance on binding to monomeric Sandercyanin variant (orange) compared to the wild-type tetrameric protein (cyan). Abstract : Biliverdin IX-alpha (BV), a tetrapyrrole, is found ubiquitously in most living organisms. It functions as a metabolite, pigment, and signaling compound. While BV is known to bind to diverse protein families such as heme-metabolizing enzymes and phytochromes, not many BV-bound lipocalins (ubiquitous, small lipid-binding proteins) have been studied. The molecular basis of binding and conformational selectivity of BV in lipocalins remains unexplained. Sandercyanin (SFP)–BV complex is a blue lipocalin protein present in the mucus of the Canadian walleye ( Stizostedion vitreum ). In this study, we present the structures and binding modes of BV to SFP. Using a combination of designed site-directed mutations, X-ray crystallography, UV/VIS, and resonance Raman spectroscopy, we have identified multiple conformations of BV that are stabilized in the binding pocket of SFP. In complex with the protein, these conformers generate varied spectroscopic signatures both in their absorption and fluorescence spectra. We show that despite no covalent anchor, structural heterogeneity of the chromophore is primarily driven by the D-ring pyrrole of BV. Our work shows how conformational promiscuity of BV is correlated to the rearrangement of amino acids in the protein matrix leading to modulation of spectral properties.