Structural basis for copper/silver binding by the Synechocystis metallochaperone CopM

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Copper homeostasis is crucial, involving sensing, storage, and efflux.
• CopM is a cyanobacterial metallochaperone linked to copper resistance.
• The molecular mechanism of copper recognition by CopM was previously unknown.

Purpose of the Study:

• To elucidate the molecular basis of copper recognition by the cyanobacterial metallochaperone CopM.
• To determine the structural basis for CopM's interaction with copper and silver ions.

Main Methods:

• X-ray crystallography was used to obtain structures of CopM.
• Structures were determined for apo, copper-bound, and silver-bound forms of CopM.

Main Results:

• Crystal structures revealed monovalent copper/silver ions bound within the protein core.
• Divalent copper ions were observed on the protein surface.
• A conserved binding site involving two consecutive histidines was identified for monovalent ions.
• Two distinct conformational states were observed, with flexibility in the first alpha-helix linked to function.

Conclusions:

• CopM utilizes a conserved histidine-based site for monovalent copper/silver binding.
• Structural flexibility in CopM is associated with its metallochaperone activity.
• This work reveals functional diversity within a simple four-helical protein family.