Functional and structural insights into astacin metallopeptidases

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Astacins are a family of metallopeptidases involved in various metabolic processes.
• They exist as secreted or membrane-anchored proteins, regulated by inactive zymogen forms and inhibitors.
• Astacin family members possess distinct structural domains, including catalytic, extracellular, transmembrane, and cytosolic regions.

Purpose of the Study:

• To review the structural architecture of astacin catalytic domains.
• To elucidate the mechanisms of zymogenic activation in astacins.
• To discuss the functional implications of astacin structural features.

Main Methods:

• Structural characterization of four astacin catalytic domains and one zymogen.
• Analysis of conserved structural elements, including zinc-binding motifs and active-site clefts.
• Investigation of activation mechanisms, such as the 'aspartate-switch' and 'tyrosine switch' motions.

Main Results:

• Astacin catalytic domains are compact, zinc-dependent moieties with distinct N-terminal and C-terminal sub-domains separated by an active-site cleft.
• They possess a conserved zinc-binding motif (HEXXHXXGXXH) characteristic of the metzincin clan.
• Pro-segments inhibit catalytic zinc via an 'aspartate-switch' mechanism, and their removal reveals an active-site cleft favoring aspartate residues.
• Structural rearrangements occur during activation and substrate/inhibitor binding, involving an 'activation domain' and a 'tyrosine switch' motion.

Conclusions:

• The structural organization of astacin catalytic domains is crucial for their enzymatic activity and regulation.
• Zymogenic activation involves significant structural rearrangements, including pro-segment removal and domain movements.
• Understanding astacin structure provides insights into metallopeptidase function and inhibition.