The Protein Journal

, Volume 32, Issue 7, pp 560–567 | Cite as

F99 is Critical for Dimerization and Activation of South African HIV-1 Subtype C Protease

  • Previn Naicker
  • Palesa Seele
  • Heini W. Dirr
  • Yasien Sayed


HIV-1 protease (PR) is an obligate homodimer which plays a pivotal role in the maturation and hence propagation of HIV. Although successful developments on PR active site inhibitors have been achieved, the major limiting factor has been the emergence of HIV drug-resistant strains. Disruption of the dimer interface serves as an alternative mechanism to inactivate the enzyme. The terminal residue, F99, was mutated to an alanine to investigate its contribution to dimer stability in the South African HIV-1 subtype C (C-SA) PR. The F99A PR and wild-type C-SA PR were overexpressed and purified. The activities of the PRs and their ability to bind an active site inhibitor, acetyl-pepstatin, were determined in vitro. The F99A PR showed no activity and the inability to bind to the inhibitor. Secondary and quaternary structure analysis were performed and revealed that the F99A PR is monomeric with reduced β-sheet content. The mutation of F99 to alanine disrupted the presumed ‘lock-and-key’ motif at the terminal dimer interface, in turn creating a cavity at the N- and C-terminal antiparallel β-sheet. These findings support the design of inhibitors targeting the C-terminus of the C-SA PR, centered on interactions with the bulky F99.


Human immunodeficiency virus Protease F99A Dimer interface Dimerization inhibitors Subtype C 



Acquired immunodeficiency syndrome


South African subtype C


Deoxyribonucleic acid


Human immunodeficiency virus


Protein data bank





This work was supported by the University of the Witwatersrand, South African National Research Foundation (Grant: NRF Thuthuka/REDIBA to Y.S; 60810, 65510 and 68898 to H.W.D) and the South African Research Chairs Initiative of the Department of Science and National Research Foundation (Grant: 64788 to H.W.D).

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  • Previn Naicker
    • 1
  • Palesa Seele
    • 1
  • Heini W. Dirr
    • 1
  • Yasien Sayed
    • 1
  1. 1.Protein Structure-Function Research Unit, School of Molecular and Cell BiologyUniversity of the WitwatersrandJohannesburgSouth Africa

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