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Protein Folding

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Proteins are chains of amino acids linked together by peptide bonds. Upon synthesis, a protein folds into a three-dimensional conformation, critical to its biological function. Interactions between its constituent amino acids guide protein folding, and hence the protein structure is primarily dependent on its amino acid sequence.
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Related Experiment Video

Updated: Oct 21, 2025

Residue-Specific Exchange of Proline by Proline Analogs in Fluorescent Proteins: How "Molecular Surgery" of the Backbone Affects Folding and Stability

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Pinholin S²¹ mutations induce structural topology and conformational changes.

Tanbir Ahammad¹, Rasal H Khan¹, Indra D Sahu²

¹Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.

Biochimica Et Biophysica Acta. Biomembranes

|September 9, 2021

Summary

Mutations in pinholin S²¹, a phage lysis timekeeper, alter its structure and function. Changes in hydrophobicity affect antipinholin domain exposure, modulating cell lysis timing and providing insights into membrane protein behavior.

Keywords:

CW-EPR power saturation DEER spectroscopy Holin Mutational effect Pinholin

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Published on: July 30, 2014

Area of Science:

Molecular Biology
Biophysics
Structural Biology

Background:

Bacteriophage lysis is regulated by a system including holin, endolysin, and spanin proteins.
Holin acts as the lysis timekeeper, with pinholin S²¹ from phage Φ21 being a key example.
Mutations in pinholin and antipinholin influence lysis timing based on growth conditions.

Purpose of the Study:

To directly investigate the structural and conformational effects of pinholin S²¹ mutations.
To correlate these structural changes with pinholin function in cell lysis timing.
To explore the impact of hydrophobicity on pinholin-antiphilin interactions.

Main Methods:

Continuous wave electron paramagnetic resonance (CW-EPR) power saturation spectroscopy.
Double electron-electron resonance (DEER) spectroscopy.
Analysis of pinholin S²¹ structure and conformational dynamics.

Main Results:

Increased hydrophilicity from mutations accelerated antipinholin transmembrane domain 1 (TMD1) externalization.
Increased hydrophobicity prevented TMD1 externalization, potentially altering pinholin S²¹ activation.
Mutations influence intra- and intermolecular interactions, affecting pinholin activation and lysis timing.

Conclusions:

Pinholin S²¹ mutation-induced hydrophobicity changes directly impact its structure and function.
This study provides a novel method for analyzing mutation effects on holin systems and other membrane proteins.
Understanding these mechanisms can lead to new strategies for controlling phage lysis.