Gas-phase behavior of noncovalent transmembrane segment complexes.

Area of Science:

• Biochemistry
• Structural Biology
• Mass Spectrometry

Background:

• Specific helix oligomerization between transmembrane segments (TMSs) is crucial for protein function.
• Motifs like GxxxG are known to promote helix oligomerization.
• Disruption of these motifs can reduce dimerization levels.

Purpose of the Study:

• To investigate the influence of sequence motifs like GxxxG on TMS oligomerization in both solution and gas phases.
• To compare the behavior of TMSs in the gas and liquid phases.
• To determine the correlation between solution structure and gas-phase dimerization.

Main Methods:

• Circular dichroism (CD) spectroscopy to determine helicity in solution.
• Electrospray mass spectrometry (ESI-MS) to monitor dimerization in the gas phase.
• Collision-induced dissociation (CID) to study complex stability in the gas phase.

Main Results:

• A direct correlation exists between solution helicity and gas-phase dimerization.
• Peptides retain memory of their liquid-phase structure in the gas phase.
• Sequence-specific oligomerization dependent on the GxxxG motif was not observed via mass spectrometry.
• Noncovalent interactions of TMSs in mass spectrometry are more dependent on secondary structure and folding than primary sequence.

Conclusions:

• Proper folding in solution is a prerequisite for TMS oligomerization.
• Gas-phase behavior of TMSs reflects their solution-phase structural properties.
• Secondary structure and proper folding play a more significant role in TMS noncovalent interactions than primary sequence motifs in mass spectrometry.