Slr0006-like proteins: A TsaC/TsaC2/YciO subfamily exclusive to cyanobacteria

- We identified a new TsaC/TsaC2/YciO subfamily called the Slr0006-like subfamily.
- The Slr0006-like proteins are found exclusively in cyanobacteria.
- Each TsaC/TsaC2/YciO subfamily has a specific signature motif in cyanobacteria.
- The Slr0006-like proteins have the typical TsaC-domain fold with a central cleft.
- The central cleft might contribute to the unique function of Slr0006-like proteins.

The universally conserved TsaC/TsaC2/YciO family of proteins is essential for the N6-threonylcarbamoyladenosine modification present in almost all ANN-decoding tRNAs. Previously, the family has been grouped into the TsaC/TsaC2 and YciO subfamilies. We used sequence analysis, phylogenetic methods and homology modeling to show that a third subfamily, the Slr0006-like subfamily, exists exclusively in some cyanobacteria. The Slr0006-like proteins are solely found together with both TsaC and YciO homologs, indicating a distinct function for the Slr0006-like subfamily. Accordingly, the homology models show that the amino acids in their putative binding clefts differ significantly. Hence, we introduce a new cyanobacterial subfamily of proteins with the TsaC-domain fold, along with the generated classification rules to assign new members to the correct cyanobacterial subfamily.

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