Cellular function of the GndA small open reading frame-encoded polypeptide during heat shock
Hundreds of bacterial small open reading frames (sORFs) encoding microproteins of fewer than fifty amino acids have recently been identified. Biological functions have been ascribed to an increasing number of microproteins, some of which play roles in bacterial stress responses. In this work, we provide evidence that GndA, a frameshifted 36-amino acid microprotein encoded in an internal open reading frame overlapping the 6-phosphogluconate dehydrogenase (6PGD) coding sequence (CDS), functions in the response to heat shock. We demonstrate independent contributions of GndA and 6PGD to cell growth at high temperature. GndA is hydrophobic and associates with the pyruvate dehydrogenase complex and respiratory complex I (RCI). Consistent with a role in cellular homeostasis, GndA mutations alter the transcriptional responses to heat shock. These results demonstrate that GndA promotes bacterial cell growth at high temperature via a mechanism distinct from that of the 6PGD protein that it overlaps. GndA thus expands the paradigm of bacterial microproteins that function in cellular stress responses.