Abstract
Proteins can coordinate metal ions with endogenous nitrogen and oxygen ligands through backbone amino and carbonyl groups, but the amino acid side chains coordinating metals do not include tryptophan. Here we show for the first time the involvement of the tryptophan metabolite kynurenine in a protein metal-binding site. The crystal structure to 1.35 angstroms of MopE* from the methane-oxidizing Methylococcus capsulatus (Bath) provided detailed information about its structure and mononuclear copper-binding site. MopE* contains a novel protein fold of which only one-third of the structure displays similarities to other known folds. The geometry around the copper ion is distorted tetrahedral with one oxygen ligand from a water molecule, two histidine imidazoles (His-132 and His-203), and at the fourth distorted tetrahedral position, the N1 atom of the kynurenine, an oxidation product of Trp-130. Trp-130 was not oxidized to kynurenine in MopE* heterologously expressed in Escherichia coli, nor did this protein bind copper. Our findings indicate that the modification of tryptophan to kynurenine and its involvement in copper binding is an innate property of M. capsulatus MopE*.
Highlights
In Methylococcus capsulatus (Bath) and other methane-oxidizing bacteria, copper is important for both regulation and catalytic activity of the particulate methane-monooxygenase (2)
When copper is present in the growth medium, methanobactin is mainly associated with the membranes, possibly in direct association with the particulate methane-monooxygenase, whereas at copperlimited growth conditions, methanobactin accumulates in the growth medium
We present here x-ray diffraction and mass spectrometry data on the M. capsulatus-secreted protein, MopE*
Summary
Values for outer shell are indicated in parenthesis. Data collection Beamline Wavelength Detector Space group Diffraction limit No molecules in asymetric unit Unit cell parameters a axis (Å) b axis (Å) c axis (Å) -Angle (°) Total no. Of reflections No of unique reflections Completeness (%) I/(I) Mean ((I)/S.D. (I)) Rmerge (%) Multiplicity Wilson B (Å2) Outer shell Data collection Beamline Wavelength Detector Space group Diffraction limit No molecules in asymetric unit Unit cell parameters a axis (Å) b axis (Å) c axis (Å) -Angle (°) Total no. of reflections No of unique reflections Completeness (%) I/(I) Mean ((I)/S.D. (I)) Rmerge (%) Multiplicity Wilson B (Å2) Outer shell
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have