Molecular, structural, and functional characterization of delta subunit of T-complex protein-1 from <i>Leishmania donovani</i>

Chaperonins/Heat shock protein 60 are ubiquitous multimeric protein complexes that assist in the folding of partially and/or misfolded proteins using metabolic energy into their native stage. The eukaryotic group II chaperonin, also referred as T-complex protein-1 ring complex (TRiC)/T-complex protein-1 (TCP1)/chaperonin containing T-complex protein (CCT), contains 8-9 paralogous subunits, arranged in each of the two rings of hetero-oligomeric complex. In <i>Leishmania</i>, till date, only one subunit, LdTCP1γ, has been well studied. Here, we report the molecular, structural, and functional characterization of TCP1δ subunit of <i>Leishmania donovani</i> (LdTCP1δ), the causative agent of Indian kala-azar. LdTCP1δ gene exhibited only 27.9% identity with LdTCP1γ and clustered in a separate branch in the phylogenic tree of LdTCP1 subunits. The purified recombinant protein formed a high molecular weight complex (0.75 MDa), arranged into 16-mer assembly, and performed <i>in vitro</i> chaperonin activity as assayed by ATP-dependent luciferase folding. LdTCP1δ exhibits 1.8-fold upregulated expression in metabolically active, rapidly dividing log phase promastigotes. Over-expression of LdTCP1δ in promastigotes results in increased infectivity and rate of multiplication of intracellular amastigotes. The study thus establishes the existence of an individual functionally active homo-oligomeric complex of LdTCP1δ chaperonin with its role in parasite infectivity and multiplication.