Defelipe, L. | Search bioRxiv

bioRxiv2024

Sla2 is a core interaction hub for Clathrin Light Chain and the Pan1/End3/Sla1Complex

The interaction network of Sla2, a vital adaptor protein in the endocytic mid-coat, undergoes constant rearrangement incorporating or replacing interacting proteins over time. Sla2 serves as a scaffold linking the membrane to the actin cytoskeleton, with this role modulated by Clathrin Light Chain (CLC), which inhibits Sla2s function under certain conditions. We show that Sla2 has two independent binding sites for CLC: one previously described in homologs of Fungi (Sla2) and Metazoa (Hip1R), and a second found only in Fungi. We present the structural model of the Sla2 actin-binding domains in the context of regulatory structural domains by electron cryo-microscopy. We provide an interaction map of Sla2 and the regulatory proteins Sla1 and Pan1, predicted by AI modelling and confirmed by molecular biophysics techniques. Pan1 competes with CLC for the conserved binding site on Sla2. These results enhance the mapping of crucial interactions at endocytic checkpoints and highlight the divergence between Metazoa and Fungi in this vital process. TeaserSla2 forms complexes with three regulatory proteins in the endocytic pit, two of which compete for the same site

molecular biology↗

bioRxiv2024

Subtleties in Clathrin Heavy Chain Binding Boxes provide selectivity among Adaptor Proteins of Budding Yeast

Clathrin, forming the triskelion network, orchestrates highly regulated cellular processes facilitating cargo internalization and trafficking in eukaryotes, with its N-terminal domain (NTD) pivotal for adaptor protein (AP) interactions. The NTD contains up to four AP-binding sites, and their roles in preferential occupancy by APs have not been addressed. Here, employing a combination of integrative biophysical and structural approaches together with in vivo functional experiments, we investigated the binding hierarchy and selectivity of adaptors for clathrin, aiming to understand the evolutionary conservation of redundant APs and their specialized roles in endocytosis and cellular trafficking mechanisms. We found that yeast epsin Ent5 displayed the highest affinity for clathrin, indicating its significant role in cellular trafficking processes. Epsins Ent1 and Ent2, which are crucial for endocytosis but described to have redundant functions, revealed distinct binding patterns; Ent1 demonstrated stronger interactions with clathrin than Ent2, explaining its functional divergence towards actin binding. Despite both having actin anchoring domains, since Ent1 is actually more stably recruited by clathrin, it would provide a better actin anchoring function. These results offer molecular insights into AP selectivity, suggesting they competitively bind clathrin while also targeting different clathrin sites.

molecular biology↗