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Identification of HIV-1 protease cleavage site in human C1-inhibitor
Marijan Gerencer1, Vitomir Burek
1Tissue typing Centre, Department of Cellular Immunology, University Hospital KBC, HR-10000 Zagreb, Kispaticeva 12, Croatia. gerencm@baxter.com
Insights
Human immunodeficiency virus type 1 (HIV-1) protease specifically cleaves the complement C1-inhibitor protein, but not C1q, C2, or C4. This cleavage occurs at a site near other known protease targets in the N-terminal region.
Area of Science:
- Biochemistry
- Immunology
- Virology
Background:
- The human complement system is crucial for innate immunity.
- Human immunodeficiency virus type 1 (HIV-1) protease is essential for viral replication.
- Understanding interactions between viral proteases and host immune proteins is vital.
Purpose of the Study:
- To investigate the susceptibility of human classical complement pathway proteins (C1q, C2, C4) and C1-inhibitor to cleavage by HIV-1 protease.
- To identify specific cleavage sites if they exist.
Main Methods:
- Purified human complement proteins (C1q, C2, C4, C1-inhibitor) were incubated with recombinant HIV-1 protease in vitro.
- Proteolytic activity was analyzed using SDS-PAGE and immunoblotting assays.
- Amino acid sequence analysis (Edman degradation) was performed on resulting fragments.
Main Results:
- HIV-1 protease demonstrated specific cleavage activity only on the C1-inhibitor.
- No cleavage was observed for C1q, C2, or C4 proteins.
- The identified cleavage site on C1-inhibitor is located between residues Leu-32 and Phe-33 in the N-terminal region.
- This site is proximate to known cleavage sites for other proteases.
Conclusions:
- HIV-1 protease can cleave the human C1-inhibitor protein.
- This interaction does not affect C1q, C2, or C4, suggesting a specific targeting of C1-inhibitor.
- The identified cleavage site's proximity to other protease targets may have implications for immune evasion strategies by HIV-1.
Abstract:
We have investigated the ability of HIV-1 protease to cleave human complement proteins of the classical complement pathway: C1q, C2 and C4 as well as the regulatory protein, C1-inhibitor. Purified complement proteins were incubated with recombinant HIV-1 protease in vitro and analyzed by SDS-PAGE and immunoblotting assay. The only cleavage site was found in N-terminal region of C1-inhibitor, and it was located between residues Leu-32 and Phe-33 as determined by amino acid sequence analysis of the 85 kDa proteolytic fragment after 12 Edman degradation cycles. The HIV-1 protease cleavage sites were not found in C1q, C2 and C4 protein. HIV-1 protease-susceptible site in N-terminal region of C1-inhibitor is very close to the cleavage sites of some other proteases that are able to induce N-terminal proteolysis of the protein.
