Crystal structure of thermally stable homodimeric cytochrome c′-β from Thermus thermophilus

Cytochrome c'-beta is a heme protein that belongs to the cytochrome P460 family and consists of homodimeric subunits with a predominantly antiparallel beta-sheet fold. Here, the crystal structure of cytochrome c'-beta from the thermophilic Thermus thermophilus (TTCP-beta) is reported at 1.74 angstrom resolution. TTCP-beta has a typical antiparallel beta-sheet fold similar to that of cytochrome c'-beta from the moderately thermophilic Methylococcus capsulatus (MCCP-beta). The phenylalanine cap structure around the distal side of the heme is also similar in TTCP-beta and MCCP-beta, indicating that both proteins similarly bind nitric oxide and carbon monoxide, as observed spectroscopically. Notably, TTCP-beta exhibits a denaturation temperature of 117 degrees C, which is higher than that of MCCP-beta. Mutational analysis reveals that the increased homodimeric interface area of TTCP-beta contributes to its high thermal stability. Furthermore, 14 proline residues, which are mostly located in the TTCP-beta loop regions, possibly contribute to the rigid loop structure compared with MCCP-beta, which has only six proline residues. These findings, together with those from phylogenetic analysis, suggest that the structures of Thermus cytochromes c'-beta, including TTCP-beta, are optimized for function under the high-temperature conditions in which the source organisms live.

Automated summary

This study reports the crystal structure of cytochrome c'-beta from Thermus thermophilus, which exhibits high thermal stability. Mutational analysis suggests that the increased homodimeric interface area and rigid loop structure contribute to its high thermal stability.