
==== Front
bioRxiv
BIORXIV
bioRxiv
2692-8205
Cold Spring Harbor Laboratory

10.1101/2024.08.22.609173
preprint
1
Article
Transmembrane channel-like 4 and 5 proteins at microvillar tips are potential ion channels and lipid scramblases
Ebrahim Seham http://orcid.org/0000-0002-6762-2432

Ballesteros Angela http://orcid.org/0000-0001-5796-6875

Sharon Zheng W.
Mukherjee Shounak
Hu Gaizun
Weng Wei-Hsiang
Montgomery Jonathan S.
Agyemang Yaw
Cui Runjia
Sun Willy
Krystofiak Evan
Foster Mark P.
Sotomayor Marcos
Kachar Bechara
23 8 2024
2024.08.22.609173https://creativecommons.org/publicdomain/zero/1.0/ To the extent possible under law, the person who associated CC0 with this work has waived all copyright and related or neighboring rights to this work.
http://biorxiv.org/lookup/doi/10.1101/2024.08.22.609173
nihpp-2024.08.22.609173.pdf
Abstract

Microvilli—membrane bound actin protrusions on the surface of epithelial cells—are sites of critical processes including absorption, secretion, and adhesion. Increasing evidence suggests microvilli are mechanosensitive, but underlying molecules and mechanisms remain unknown. Here, we localize transmembrane channel-like proteins 4 and 5 (TMC4 and 5) and calcium and integrin binding protein 3 (CIB3) to microvillar tips in intestinal epithelial cells, near glycocalyx insertion sites. We find that TMC5 colocalizes with CIB3 in cultured cells and that a TMC5 fragment forms a complex with CIB3 in vitro . Homology and AlphaFold2 models reveal a putative ion permeation pathway in TMC4 and 5, and molecular dynamics simulations predict both proteins can conduct ions and perform lipid scrambling. These findings raise the possibility that TMC4 and 5 interact with CIB3 at microvillar tips to form a mechanosensitive complex, akin to TMC1 and 2, and CIB2 and 3, within the mechanotransduction channel complex at the tips of inner ear stereocilia.
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