Abstract
Protein-l-isoaspartate O-methyltransferase (PIMT), encoded by PCMT1, is a repair enzyme that corrects isoaspartyl lesions, preserving protein structure and function. While indispensable for neuronal integrity, its role in red blood cells (RBCs) and transfusion outcomes is incompletely understood. Here, we show that novel erythroid-specific Pcmt1 knockout mice display profound remodeling of one-carbon metabolism, accumulation of repair intermediates, and destabilization of glycolytic and cytoskeletal proteins, yet maintain lower lipid peroxidation and normal post-transfusion recovery. Analysis of 13,091 blood donors from the Recipient Epidemiology and Donor Evaluation Study (REDS)-III Red Blood Cell Omics (RBC Omics) study revealed that common PCMT1 variants associate with hemolysis phenotypes and regulate PIMT protein level, as gleaned by protein quantitative trait loci (pQTL) analyses. The nonsynonymous rs4816 (V120I) allele, enriched in donors of Asian or African ancestry, emerged as a beneficial variant: carriers exhibited lower osmotic hemolysis, altered peptide methylation flux, and higher PIMT protein levels. Recombinant expression confirmed that the I120 variant displays preserved global folding, but greater catalytic activity than the canonical V120 enzyme. Transfusion outcome data showed that PCMT1 genotype influences hemoglobin increments and bilirubin responses in recipients. These findings identify PIMT as a novel determinant of RBC storage biology and establish rs4816 as a protective allele, with broader implications for donor diversity, transfusion efficacy, and proteome maintenance in aging.