β37Trp → Cys mutation leads to multiple new hemoglobin species in red cells

ObjectivesTo determine the cause of an unusual hemoglobin (Hb) pattern detected during HbA1c monitoring.Design and methodHemolysate was analysed by ESI MS, and individual components purified by reverse phase HPLC. Peptide mapping was used to pinpoint the substitution and DNA sequencing to confirm the mutation.ResultsESI MS of lysate showed three novel β chains with mass changes of − 83, − 51 and + 222 Da. Peptide mapping and DNA sequencing indicated a β37Trp→Cys substitution. Reverse phase chromatography showed three new β globins eluting ahead of βAConclusionThe new Hbs result from an initial β37Trp→Cys mutation (− 83 Da) followed by oxidation to cysteine sulfinic acid (+ 32 Da) and the formation of a glutathione adduct (+ 305 Da). Despite the hydrophobicity change and the critical location of the side chain on the α1β2 interface, there was no evidence of molecular instability or altered oxygen affinity, and no clear phenotype apart from discordant HbA1c.

► Novel Hb Beta chain variant found confounding HbA1c estimation.
► Trp37Cys mutation results in the production of three new beta globins.
► Conversion of Cys to Cys sulfinic acid.
► Huge change at highly conserved amino acid residue.
► No alteration in stability or oxygen affinity.