Convergent construction of N-terminally modified CCL5 chemokines for photoaffinity receptor pull-down using cross-aldol bioconjugations.

Chemokines such as CCL5 (RANTES) mediate immune responses via interaction with G-protein-coupled receptors like CCR5, which also serves as a co-receptor for HIV-1 entry into host cells. Modified CCL5 analogues have shown promise as CCR5 antagonists for anti-HIV strategies, but current approaches involve hydrolytically unstable linkages or laborious synthesis. Here, we demonstrate the use of an organocatalyst-mediated protein aldol ligation (OPAL) to construct N-terminally modified CCL5 analogues bearing hydrolytically stable carbon-carbon linkages. Using a recombinant CCL5 P2G mutant and selective oxidation to introduce an α-oxo aldehyde at the N-terminus, we achieved efficient OPAL bioconjugation with various aldehyde donors, including alkyl and aryl acetaldehydes. Notably, a 4-azido aryl acetaldehyde CCL5 OPAL product was utilised as a CCR5 photoaffinity probe. This modified chemokine successfully captured CCR5 from mammalian cells via photo-crosslinking, enabling receptor pull-down for biochemical analysis. Our work showcases cross-aldol bioconjugations as a versatile and convergent strategy for stable chemokine functionalisation, with potential applications in therapeutic development and mechanistic studies of chemokine-receptor interactions. This method offers a promising chemical biology platform for modulating or probing the CCL5-CCR5 axis with enhanced precision and synthetic accessibility.