Related Experiment Videos
Crystal structures of MS2 capsids with mutations in the subunit FG loop
N J Stonehouse1, K Valegård, R Golmohammadi
1Department of Genetics, University of Leeds, UK.
Abstract:
The loop between the F and G beta strands (FG loop) of the bacteriophage MS2 coat protein subunit forms inter-subunit contacts around the 5-fold and 3-fold (quasi 6-fold) axes of the T=3 protein shell. In capsids, the loop is found in two very different conformations, one in B subunits, which form the 5-fold contact, and one in A and C subunits, which form the quasi 6-fold contact. One proline residue, Pro78, is strictly conserved in the coat protein of all related bacteriophages, and in the case of MS2 this proline residue is preceded by a cis peptide bond in the B subunit. In order to probe the role of the FG loop in capsid assembly, we have determined the crystal structures of two MS2 capsids, formed by coat proteins with mutations at two positions in the FG loop, P78N or E76D. These mutants show conformational changes in the FG loops that explain the reduced temperature stability of the capsids. The P78N mutant has a normal trans peptide bond at position 78.
Insights
Mutations in the MS2 bacteriophage coat protein FG loop alter its conformation, affecting capsid assembly and stability. Proline 78
Area of Science:
- Structural biology
- Virology
- Biochemistry
Background:
- The bacteriophage MS2 coat protein forms a T=3 capsid shell.
- The F and G beta strands (FG loop) mediate inter-subunit contacts.
- FG loop conformations differ between subunit types (A/C vs. B).
Purpose of the Study:
- To investigate the role of the FG loop in MS2 capsid assembly.
- To understand the structural basis of capsid temperature stability.
- To probe the function of conserved proline residue Pro78.
Main Methods:
- X-ray crystallography of MS2 capsids.
- Site-directed mutagenesis of coat protein FG loop (P78N, E76D).
- Analysis of capsid structure and stability.
Main Results:
- Mutations P78N and E76D induced conformational changes in FG loops.
- These changes correlate with reduced capsid temperature stability.
- The P78N mutation resulted in a trans peptide bond, unlike the wild-type cis bond.
Conclusions:
- The FG loop conformation is critical for MS2 capsid assembly and stability.
- Proline 78 and its preceding peptide bond configuration influence structural integrity.
- Mutations impacting FG loop structure compromise capsid thermal stability.