Conservation of Binding of Llama and Other Animals’ Hemoglobins to Haptoglobins Across Species

The plasma protein haptoglobin binds hemoglobin released from lysed erythrocytes. It causes removal of the free hemoglobin, thus preventing pathological oxidation of cells. Hemoglobin higher level structures are well conserved across animal species but primary structures can be as little as 50% homologous. Because of these differences, the question arose as to what extent hemoglobins can bind to haptoglobins from different species. The charge properties and binding to three genetic variants of human haptoglobin were compared by non-denaturing agarose gel electrophoresis, with llama, human, dog, pig, horse and goat hemoglobins. In this study, it was reported for the first time that llama and alpaca hemoglobins differed in electrophoretic mobility from hemoglobins from several animal species and humans. Llama hemoglobin was more positively charged than the other mammalian hemoglobins. Electrophoretic mobility changes of the animal hemoglobins in the presence of human plasma and two different purified human haptoglobin genetic variants suggested that hemoglobins from all animals in this study could bind all three genetic variants of human haptoglobin. In all cases, the llama hemoglobin-haptoglobin samples had lesser mobility than those of the other mammals. This study showed that the binding sites on hemoglobin and haptoglobin for each other have been evolutionarily conserved despite differences in primary structure and marked difference in the charge of llama hemoglobin from the other animal species and humans.