# Signal-strapping as a protein-sequence search method for the discovery of metalloproteins

## TL;DR

A new method called signal strapping helps discover metalloproteins by searching for proteins with an N-terminal histidine that binds metal ions.

## Contribution

Signal strapping is introduced as a novel proteomic search method for discovering metalloproteins based on N-terminal histidine residues.

## Key findings

- Signal strapping identifies proteins with N-terminal histidine capable of coordinating metal ions.
- Four classes of bacterial metalloproteins were discovered and characterized using this method.
- Two newly identified metalloproteins are named anglerases due to their ability to capture transition metal ions.

## Abstract

Metalloprotein discovery is often made post hoc, in which activity studies following protein isolation reveal a metal-ion dependence. Herein we take a different approach to finding metalloproteins, by building on the discovery of copper-containing lytic polysaccharide monooxygenases (LPMOs), which include an N-terminal histidine as part of their sequence. This residue acts as a natural chelator for transition metal ions, irrespective of the structure of the protein. We report the method of signal strapping, where sequences of N-terminal signal peptides artificially appended with a histidine residue at their C-terminus are used to bootstrap a proteomic search. These searches return sequences of proteins with an N-terminal histidine capable of coordinating a metal ion. We exemplify the approach by the discovery and characterisation of four classes of bacterial metalloproteins, including two that we denote as anglerases reflecting their potential to capture transition metal ions from the bacterial environment.

Signal peptide sequences appear in secreted proteins. Here, authors use these sequences in a proteomic search method called “signal strapping” to discover metalloproteins, which have an N-terminal histidine that chelates a transition metal ion.