Biology subjects

DeCosta, A.

Publications and source records attributed to DeCosta, A..

3 recordsLinked to original sources

bioRxiv2026

A mitochondrial insertion directs substrate selection and engagement by ClpX

The force-generating AAA+ ATPase domain of protein unfoldases is specified for many substrates and other functional partners through elaboration with accessory domains. Mitochondrial homologs of the unfoldase ClpX contain an insertion within the AAA+ domain that is absent in bacterial homologs. This mitochondrial insertion (MI) maps to the substrate-encountering face of ClpX, leading us to hypothesize that the MI directs interactions of ClpX with mitochondrial substrates, the best-characterized of which is the first enzyme in heme biosynthesis, ALAS. We find that the MI is critical for both recruitment and activation of ALAS by S. cerevisiae ClpX. The MI was dispensable for heme-induced, adaptor-mediated degradation of ALAS by human CLPXP, but contributed to adaptor-independent recruitment of the model substrate casein for degradation. Although truncation of the MI moderately perturbed ATPase activity in both yeast and human ClpX, this effect could be uncoupled from the requirement for the MI in the efficiency of ALAS activation by targeted mutagenesis. The MI therefore can serve both to recruit a substrate to mitochondrial ClpX and to accelerate its processing by the AAA+ motor.

biochemistry↗

bioRxiv2024

An adaptor for feedback regulation of heme biosynthesis by the mitochondrial protease CLPXP

Heme biosynthesis is tightly coordinated such that essential heme functions including oxygen transport, respiration, and catalysis are fully supplied without overproducing toxic heme precursors and depleting cellular iron. The initial heme biosynthetic enzyme, ALA synthase (ALAS), exhibits heme-induced degradation that is dependent on the mitochondrial AAA+ protease complex CLPXP, but the mechanism for this negative feedback regulation had not been elucidated. By biochemical reconstitution, we have discovered that POLDIP2 serves as a heme-sensing adaptor protein to deliver ALAS for degradation. Similarly, loss of POLDIP2 strongly impairs ALAS turnover in cells. POLDIP2 directly recognizes heme-bound ALAS to drive assembly of the degradation complex. The C-terminal element of ALAS, truncation of which leads to a form of porphyria (XLDPP), is dispensable for interaction with POLDIP2 but necessary for degradation. Our findings establish the molecular basis for heme-induced degradation of ALAS by CLPXP, establish POLDIP2 as a substrate adaptor for CLPXP, and provide mechanistic insight into two forms of erythropoietic protoporphyria linked to CLPX and ALAS.

biochemistry↗

bioRxiv2021

Structural basis of malaria transmission blockade by a monoclonal antibody to gamete fusogen HAP2

HAP2 is a transmembrane gamete fusogen found in multiple eukaryotic kingdoms and is structurally homologous to viral class II fusogens. Studies in Plasmodium have suggested that HAP2 is an attractive target for vaccines that block transmission of malaria. HAP2 has three extracellular domains, arranged in the order D2, D1, and D3. Here, we report monoclonal antibodies against the D3 fragment of Plasmodium berghei HAP2 and crystal structures of D3 in complex with Fab fragments of two of these antibodies, one of which blocks fertilization of Plasmodium berghei in vitro and transmission of malaria in mosquitos. We also show how this Fab binds the complete HAP2 ectodomain with electron microscopy. The two antibodies cross-react with HAP2 among multiple plasmodial species. Our characterization of the Plasmodium D3 structure, HAP2 ectodomain architecture, and mechanism of inhibition provide insights for the development of a vaccine to block malaria transmission.

immunology↗