Alpha secondary structures generate weak but recurrent periodicity in proteins

Area of Science:

• Structural Biology
• Protein Science
• Biophysics

Background:

• Many proteins display weak, recurrent periodic patterns in their residue sequences.
• Previous observations suggested these patterns might originate from ancient, regular sequences.
• The significance of periodicity at specific residue intervals (i+4, i+7, i+11) has been noted.

Purpose of the Study:

• To investigate the origin and location-specific nature of weak periodic patterns in protein sequences.
• To determine if periodicity is a general feature of all protein structures or specific to certain secondary structures.
• To explore the potential physical basis for observed periodic patterns in proteins.

Main Methods:

• Statistical analysis of residue similarity at specific intervals (i+4, i+7, i+11) across large protein datasets.
• Comparative analysis of periodicity within alpha-helical versus beta-stranded protein subregions.
• Correlation analysis between periodicity and the distribution of hydrophobic residues.

Main Results:

• Weak periodic patterns were significantly detected in protein sequences, especially within alpha-helical regions.
• No significant periodic patterns were found in beta-stranded subsequences.
• The regular alternation of hydrophobicity, a common feature of alpha helices, strongly correlates with the observed weak periodicity.

Conclusions:

• The recurrent weak periodicity in proteins is not primarily due to ancestral periodic sequences.
• Alpha-helical structures are the main location for this periodicity, suggesting a structural basis.
• The intrinsic physical property of alternating hydrophobicity in alpha helices is the likely origin of the observed weak periodic patterns.