Phage spanins: diversity, topological dynamics and gene convergence

Area of Science:

• Microbiology
• Structural Biology
• Bioinformatics

Background:

• Spanins are phage lysis proteins crucial for disrupting the Gram-negative bacterial outer membrane.
• Two types exist: two-component (i-spanin and o-spanin) and unimolecular spanins, differing in genetic architecture and topology.
• Both spanin types facilitate the fusion of the inner and outer membranes for progeny virion release.

Purpose of the Study:

• To create a comprehensive database of spanins.
• To analyze the structural diversity and evolutionary dynamics of spanins.
• To elucidate conserved functional motifs and mechanisms.

Main Methods:

• Bioinformatic analysis of 586 identified spanins (528 two-component, 58 unimolecular).
• Sequence identity threshold (40% identity over 40% length) for family grouping.
• Multiple sequence alignments and secondary structure predictions.
• Experimental verification of a novel lipobox motif.

Main Results:

• SpaninDataBase contains 528 two-component and 58 unimolecular spanins.
• Significant differences in secondary structures observed between spanin types and architectures.
• 143 i-spanin, 125 o-spanin, and 13 u-spanin families identified, with high prevalence of singletons indicating extreme diversity.
• Conserved secondary structure patterns and domain organization within families.
• Evolutionary dynamics of gene arrangement elucidated.
• Evidence for intermolecular disulfide bonds in two-component spanin function.
• A novel lipobox motif, AWAC, was identified and verified.

Conclusions:

• Bioinformatic insights into spanin function, evolution, and domain organization.
• SpaninDataBase serves as a platform for future research.
• Spanins employ diverse strategies, akin to viral fusion proteins, to achieve membrane fusion.