Structure-based characterization of canine-human chimeric uricases and its evolutionary implications

Area of Science:

• Evolutionary biology
• Biochemistry
• Genetics

Background:

• Uricase, an enzyme that breaks down uric acid, was lost in hominoids during primate evolution.
• The exact mechanism of uricase inactivation in humans and great apes remains debated, with single mutation events proposed.

Purpose of the Study:

• To investigate the inactivation process of hominoid uricase.
• To identify specific mutations responsible for the loss of uricase activity in primates.

Main Methods:

• Construction of chimeric uricase enzymes between canine and human sequences.
• Analysis of enzymatic characteristics of chimeric uricases.
• Utilizing homology modeling, site-directed mutagenesis, and DNA alignment to pinpoint critical mutations.

Main Results:

• A single missense mutation (Arg119His) at codon 119, conserved in functional mammalian uricases, was identified as significantly reducing enzyme stability and likely causing initial inactivation.
• This Arg119His mutation, shared by humans and great apes, is proposed as the primary event, preceding a later nonsense mutation at codon 33 that silenced the gene.
• Deleterious structural mutations, like Val296Ala in canine uricase, are common in mammalian uricases, suggesting a broader evolutionary trend of reduced uricase activity.
• Evidence suggests prior deleterious structural changes in ancestral primates before complete uricase inactivation.

Conclusions:

• The loss of hominoid uricase was a progressive, multi-step evolutionary event, not caused by a single mutation.
• The Arg119His mutation likely initiated uricase inactivation in the human and great ape lineage.
• A general evolutionary tendency towards reduced uricase activity is observed across mammals.