title: Evidence supporting the requirement for two proline residues for expression of c.
abstract: BACKGROUND
  In humans, c antigen expression is associated with a proline residue at amino acid position 103 in the second extracellular loop of the CE protein. Comparison of nonhuman primate Rh proteins suggested that c reactivity might actually involve two proline residues. It has been shown that the RBCs of New World capuchin monkeys (Cebus apella) react with anti-c. To further define the amino acid residues involved in c expression, Rh cDNA from the capuchin was analyzed.
  
  
  METHODS
  Rh transcripts were amplified by reverse transcription PCR from RNA isolated from the reticulocytes of a capuchin monkey and were cloned and sequenced.
  
  
  RESULTS
  Rh transcripts from the capuchin monkey, whose RBCs react with anti-c, were found to encode adjacent proline residues at 102 and 103.
  
  
  CONCLUSIONS
  Sequencing of Rh transcripts from the capuchin monkey supports the hypothesis that the expression of c requires two adjacent proline residues. Proline causes bends or loops in proteins, which, in this case, might form a unique, stable structure resistant to perturbations induced by changes in upstream or downstream residues. This would explain the scarcity in humans of c variants as compared to the other major Rh antigen variants, and the preservation of c reactivity despite 24-percent divergence between the human and capuchin Rh proteins.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. Westhoff@mail.med.upenn.edu
authors.forename: C M
authors.initials: CM
authors.lastname: Westhoff
authors.forename: L E
authors.initials: LE
authors.lastname: Silberstein
authors.forename: D E
authors.initials: DE
authors.lastname: Wylie
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D002428:Cebus; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics; D006071:Gorilla gorilla; D006801:Humans; D006922:Hylobates; D008251:Macaca; D015514:Oncogene Proteins, Fusion / Q000737:chemistry / Q000235:genetics; D002679:Pan troglodytes; D011392:Proline / Q000737:chemistry*; D011993:Recombinant Fusion Proteins; D012204:Rh-Hr Blood-Group System / Q000235:genetics* / Q000276:immunology; D017386:Sequence Homology, Amino Acid
chemical_list: D000911:Antibodies, Monoclonal; D006023:Glycoproteins; D015514:Oncogene Proteins, Fusion; C066468:RHCE protein, human; D011993:Recombinant Fusion Proteins; D012204:Rh-Hr Blood-Group System; C117760:RhD fusion protein, human; C026410:Rho(D) antigen; D011392:Proline