Analysis of C3b/C4b receptor (CR1) polymorphic variants by tryptic peptide mapping |
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| Authors: | M W Nickells T Seya V M Holers J P Atkinson |
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| Affiliation: | 1. Comparative Neuroanatomy Laboratory, Department of Biology, Ecology and Earth Sciences (DiBEST), University of Calabria, Ponte Pietro Bucci 4B, Arcavacata di Rende, 87036 Cosenza, Italy;2. Department of Health Science, University Magna Graecia of Catanzaro, 88100 Catanzaro, Italy;3. Cellular and Molecular Cardio-Vascular Patho-Physiology, Department of Biology, Ecology and Earth Sciences (DiBEST), University of Calabria, Ponte Pietro Bucci 4B, Arcavacata di Rende, 87036 Cosenza, Italy;4. Rheumatology Research Unit, Department of Health Sciences, Magna Graecia University of Catanzaro, Edificio delle Bioscienze-Viale Europa, 88100 Catanzaro, Italy;5. Genetics and Microbiology Laboratory, Department of Biology, Ecology and Earth Sciences (DiBEST), University of Calabria, Ponte Pietro Bucci 4B, Arcavacata di Rende, 87036 Cosenza, Italy;6. Genetics, Department of Biology, Ecology and Earth Sciences (DiBEST), University of Calabria, Ponte Pietro Bucci 4B, Arcavacata di Rende, 87036 Cosenza, Italy;7. Health Center s.r.l., 87100 Cosenza, Italy;8. Department of Pharmacy and Science of Health and Nutrition, Edificio Polifunzionale University of Calabria, Arcavacata di Rende, 87036 Cosenza, Italy;9. Institute of Membrane Technology, National Research Council of Italy, ITM-CNR, c/o University of Calabria, Arcavacata di Rende, 87036 Cosenza, Italy |
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| Abstract: | The human C3b/C4b receptor (CR1) binds the major activation and opsonic fragments of the third (C3) and fourth (C4) components of complement. CR1 is a single chain integral membrane glycoprotein widely distributed on peripheral blood cells. Four codominantly inherited allelic variants with Mrs of 160,000, 190,000, 220,000 and 250,000 have been described. To address the structural basis for this unusual polymorphism, CR1 from donors expressing three of the four allelic variants was purified from surface labeled (125I) erythrocytes by iC3-Sepharose affinity chromatography and the variants compared by tryptic peptide mapping (TPM). The TPMs of each variant contained the same major peaks and minor peak areas and were nearly identical to one another. Tryptic peptide mappings of the 190,000 Mr erythrocyte CR1, which was purified prior to iodination, were similar to those derived from surface iodinated CR1. The TPMs of erythrocyte and granulocyte CR1 from the same donor differed by a single peak of increased prominence in the granulocyte map. These results indicate a conservation in amino acid sequence for those peptides detected. In view of these data and those of other studies of the structure and genetics of CR1 and related proteins, it is suggested in this paper that the allelic variation relates to CR1, being composed of repeating amino acid sequences. |
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