Journal of Molecular Evolution

, Volume 5, Issue 4, pp 291–305

Immunological comparison of azurins of known amino acid sequence

Dependence of Cross-Reactivity upon Sequence Resemblance
  • A. B. Champion
  • K. L. Soderberg
  • A. C. Wilson
  • R. P. Ambler
Article

DOI: 10.1007/BF01732216

Cite this article as:
Champion, A.B., Soderberg, K.L., Wilson, A.C. et al. J Mol Evol (1975) 5: 291. doi:10.1007/BF01732216

Summary

To examine further the dependence of immunological cross-reactivity on sequence resemblance among proteins, we carried out micro-complement fixation studies with rabbit antisera to bacterial azurins of known amino acid sequence. There is a strong correlation (r = 0.9) between number of amino acid substitutions and degree of antigenic difference (immunological distance) among these azurins. The antigenic effects of amino acid substitutions are thus approximately equal and approximately additive. Similar observations and inferences were made before with a series of bird lysozymes. Indeed, the same approximate relationship between immunological distance (y) and percent difference in amino acid sequence (x) holds for both azurins and lysozymes, namely y ≃ 5x.

An explanation is given for the dependence of immunological cross-reactivity on sequence resemblance among proteins. This entails reviewing evidence regarding the nature and number of antigenic sites on globular protein antigens as well as evidence for the existence of evolutionary biases against substitutions that are internal or cause large conformational changes. The explanation we give may apply only to those naturally occurring, globular, monomeric, isofunctional proteins whose sequences differ substantially from that of any rabbit protein.

Key words

Micro-Complement FixationImmunodiffusionHaemoglobinCytochrome cLysozymeProtein Evolution

Copyright information

© Springer-Verlag 1975

Authors and Affiliations

  • A. B. Champion
    • 1
  • K. L. Soderberg
    • 1
  • A. C. Wilson
    • 1
  • R. P. Ambler
    • 2
  1. 1.Department of Biochemistry and Department of Bacteriology and ImmunologyUniversity of CaliforniaBerkeleyUSA
  2. 2.Department of Molecular BiologyUniversity of EdinburghUSA