Structure-function-evolution of H-NS-like proteins

The three-dimensional structure of H-NS protein has not been yet determined, excepted for the C-terminal domain. Nevertheless, in silico analysis suggests that this protein contains 2 domains: the N-terminal part is predicted to be mainly a-helical and to adopt a coiled-coil structure which could play a role in oligomerisation and the C-terminal DNA-binding domain which is predicted as a mixed a-b structure. (Figure 6)

A

Figure 6: Prediction of secondary structure by the MLRC method (A) and of coiled-coil structure by the COILS program (B).

In silico analysis performed on H-NS-like proteins of various microorganisms (6,7,9,10) but also in vivo experiments (complementation of phenotypic alterations associated with a hns mutation in E. coli) suggest that they are structurally related (7).
The C-terminal part which is the most conserved region has been demonstrated to interact with DNA (Figure 7).

All proteins show a preferential binding to curved DNA and, despite a low conservation in their N-terminal part, an ability to dimerize in vitro. These results demonstrate that a family of proteins structurally and functionally related to H-NS of E. coli exists in microorganisms, at least in Gram-negative bacteria (6,7,9,10).

Figure 7: Amino acid sequence alignment of the C-terminal domain of H-NS and related proteins. Strictly conserved residues are indicated in red. (10)