The Remarkable Dual-Level Diversity of Prokaryotic Flagellins.

Dalong Hu,Peter R Reeves,Olga Zhaxybayeva

doi:10.1128/msystems.00705-19

Abstract

Flagellin, the agent of prokaryotic flagellar motion, is very widely distributed and is the H antigen of serology. Flagellin molecules have a variable region that confers serotype specificity, encoded by the middle of the gene, and also conserved regions encoded by the two ends of the gene. We collected all available prokaryotic flagellin protein sequences and found the variable region diversity to be at two levels. In each species investigated, there are hypervariable region (HVR) forms without detectable homology in protein sequences between them. There is also considerable variation within HVR forms, indicating that some have been diverging for thousands of years and that interphylum horizontal gene transfers make a major contribution to the evolution of such atypical diversity.IMPORTANCE Bacterial and archaeal flagellins are remarkable in having a shared region with variation in housekeeping proteins and a region with extreme diversity, perhaps greater than for any other protein. Analysis of the 113,285 available full-gene sequences of flagellin genes from published bacterial and archaeal sequences revealed the nature and enormous extent of flagellin diversity. There were 35,898 unique amino acid sequences that were resolved into 187 clusters. Analysis of the Escherichia coli and Salmonella enterica flagellins revealed that the variation occurs at two levels. The first is the division of the variable regions into sequence forms that are so divergent that there is no meaningful alignment even within species, and these corresponded to the E. coli or S. enterica H-antigen groups. The second level is variation within these groups, which is extensive in both species. Shared sequence would allow PCR of the variable regions and thus strain-level analysis of microbiome DNA.

Highlights

Flagellin, the agent of prokaryotic flagellar motion, is very widely distributed and is the H antigen of serology
The flagellum is made from thousands of flagellin molecules that form a helical supercoil structure, which is attached to a complex membrane-embedded basal body that rotates and imparts this rotation to the flagellum
The flagellum is generated by successive transfer of flagellin molecules into the hollow core of the preassembled basal body and their transport through the basal body and the growing flagellum to the tip of the flagellum, where they extend the flagellum by condensing onto the previous tip flagellin molecule

Summary

Introduction

The agent of prokaryotic flagellar motion, is very widely distributed and is the H antigen of serology. The first is the division of the variable regions into sequence forms that are so divergent that there is no meaningful alignment even within species, and these corresponded to the E. coli or S. enterica H-antigen groups. Domains D0 and D1 are present in all bacterial flagellins They are responsible for the structure described above, which assembles into the helical supercoil of the flagellum, and the sequences are conserved within and between species, with divergence similar to that of core genes. There are 114 H antigens in the S. enterica serotyping scheme, but many of them are in sets with closely related sequences [15] Maintenance of this diversity is generally attributed to occasional selection for an alternative structure to avoid host immunity or attack from bacteriophages or predators such as amoeba, for example. It was shown that while the central regions generally had divergent sequences in antigenically different H types, there was relatively little sequence variation within each H type [14]

Methods

Results

Conclusion