The bacteriohemerythrin from Methylococcus capsulatus (Bath): Crystal structures reveal that Leu114 regulates a water tunnel

• The crystal structure shows the existence of a putative water tunnel in McHr.
• The water tunnel in the protein facilitates the autoxidation of McHr.
• L114 at the end of water tunnel is controlling access of H2O to the di-iron core.
• Insights into the control of the autoxidation are derived from protein structures.

The bacteriohemerythrin (McHr) from Methylococcus capsulatus (Bath) is an oxygen carrier that serves as a transporter to deliver O2 from the cytosol of the bacterial cell body to the particulate methane monooxygenase residing in the intracytoplasmic membranes for methane oxidation. Here we report X-ray protein crystal structures of the recombinant wild type (WT) McHr and its L114A, L114Y and L114F mutants. The structure of the WT reveals a possible water tunnel in the McHr that might be linked to its faster autoxidation relative to hemerythrin in marine invertebrates. With Leu114 positioned at the end of this putative water tunnel, the hydrophobic side chain of this residue seems to play a prominent role in controlling the access of the water molecule required for autoxidation. This hypothesis is examined by comparing the autoxidation rates of the WT McHr with those of the L114A, L114Y and L114F mutants. The biochemical data are correlated with structural insights derived from the analysis of the putative water tunnels in the various McHr proteins provided by the X-ray structures.

X-ray crystal structures are reported for the bacteriohemerythrin (McHr) of Methylococcus capsulatus (Bath) and several mutants. The study provides evidence for the existence of a putative water tunnel with an essential Leu at the end of the tunnel controlling access of a water molecule to the di-iron site for autoxidation.Figure optionsDownload as PowerPoint slide