Rhesus factors: structure-function analysis and physiological role in mouse

mediate ammonium transport. Ammonium is an important nitrogen source for the

biosynthesis of amino acids for instance but its accumulation is also known as cytotoxic in

animals. Nevertheless, the controlled disposal of ammonium in urine plays a critical role in

the regulation of the acid-base homeostasis. Alteration in ammonium transport via human Rh

proteins could have clinical outcomes. In this work, we addressed aspects of structurefunction

analysis of altered human Rhesus proteins using a heterologous expression system

and further characterized aspects of the patho-physiological roles of Rh proteins using

knockout mice models available in the laboratory.

Using a yeast-based expression assay, we characterized human Rh variants resulting from non

synonymous single nucleotide polymorphisms (nsSNPs) with known or unknown clinical

phenotypes. The HsRhAG variants (I61R, F65S) associated to overhydrated hereditary

stomatocytosis (OHSt), a disease affecting erythrocytes, proved affected in intrinsic

bidirectional ammonium transport, suggesting altered ammonium transport as a potential

hallmark of the disease. Moreover, these variants showed trans-dominant negative effects on

the activity of their native HsRhAG counterpart, suggesting altered cooperation of the

subunits in “heteromeric” transport complexes. On the other hand, we revealed that the

R202C variant of HsRhCG, the orthologue of mouse Rhcg required for optimal urinary

ammonium excretion and blood pH control, shows an impaired inherent ammonium transport

activity. HsRhCGR202C may potentially confer susceptibility to disorders leading to metabolic

acidosis for instance.

MmRhcg has been shown to be expressed in the male mice epididymal tract, its absence

leading to a more acidic luminal fluid and to a reduced male fertility. Using mice

models, we further investigated the role of Rhcg and Rhbg proteins in the male

reproductive function.