Human-specific evolutionary genetic loss of addition of a single oxygen atom from sialic acids increases hydrophobicity of cells and proteins.

Humans, unlike all old world primates studied to date, lack N-glycolyl neuraminic acid (Neu5Gc: Gc) due to the evolutionary genomic loss of CMP-N-acetylneuraminic acid hydroxylase (CMAH), leading to accumulation of the N-acetyl neuraminic acid (Neu5Ac: Ac). Given the high sialic acid density on cell surfaces, we hypothesized that the ratio of Ac/Gc could influence hydrophobicity. Herein, we employed surface wetting experiments and atomic force microscopy (AFM) to investigate the hydrophobicity of Neu5Ac and Neu5Gc at the surface, protein, and cellular levels. A 5 ± 2° difference in the wetting angle of Ac/Gc-coated surfaces confirmed the greater hydrophilicity of Neu5Ac compared to Neu5Gc. AFM studies using a hydrophobically modified probe and plasma sialoglycoproteins, as well as human lymphoma cells engineered to express varying amounts of Neu5Ac or Neu5Gc, demonstrated that both proteins and cells expressing Neu5Ac exhibit a higher frequency of hydrophobic interactions with the AFM probe than those expressing Neu5Gc. These findings suggest that the loss of a single oxygen atom in sialic acid during human evolution may have significantly influenced hydrophobic properties, contributing to alterations in binding affinity and molecular interactions.