# Identification of amino acids essential for angulin‐1/3 binding of the tricellular tight junction binder, angubindin‐1

## TL;DR

This study identifies key amino acids in angubindin-1 that are essential for its binding to angulin-1/3, which could help in developing targeted drug delivery methods.

## Contribution

The paper identifies six specific amino acid residues in angubindin-1 critical for its function as a tricellular tight junction modulator.

## Key findings

- Alanine scanning revealed six essential residues (L562, L598, E638, V640, Y643, K644) in angubindin-1 for angulin binding.
- Mutants with these residues substituted showed reduced binding and loss of tTJ-modulating activity.
- These findings could aid in designing noninvasive therapeutics using angubindin-1 as a model.

## Abstract

Tight junctions (TJs) are formed where two or three cells meet and are therefore categorized, respectively, into bicellular TJs (bTJs) and tricellular TJs (tTJs). Angubindin‐1 is the first tTJ modulator enhancing intestinal macromolecule permeation via binding to the key tTJ proteins, angulin‐1 and angulin‐3. It is a fragment (amino acids 421–664) derived from domain IV of Clostridium perfringens iota toxin. Here, we identified critical residues (L562, L598, E638, V640, Y643, K644) of angubindin‐1 to be essential for binding to angulins by alanine scanning. Mutants substituting these amino acids with alanine exhibited reduced binding to angulin‐expressing cells. Simultaneous substitution of all these amino acids lost binding to angulins and resulted in the loss of tTJ‐modulating functions of angubindin‐1. These insights highlight crucial residues for the tTJ‐modulating activity of angubindin‐1, which may hold promise in the design of noninvasive, targeted therapeutics using angubindin‐1 as a prototype tTJ modulator to enhance the permeation of drugs.

Angubindin‐1 binds angulin‐1/‐3 at tricellular tight junctions, enhancing intestinal macromolecule permeation. Alanine scanning identified six essential residues (L562, L598, E638, V640, Y643, and K644) of angubindin‐1 critical for binding to angulin‐1/‐3 and permeation‐enhancing activity, providing insights for the development of targeted noninvasive drug delivery strategies.