Functional characterization of the protease of human endogenous retrovirus, K10: can it complement HIV-1 protease?
To investigate the biochemical properties of the protease encoded by the human endogenous retrovirus, K10 (HERV-K), 213 amino acids of the 3'-end of the HERV-K protease (PR) open reading frame were expressed in Escherichia coli. Autocatalytic cleavage of the expressed polypeptide resulted in an 18.2 kDa protein which was shown to be proteolytically active against a fluorogenic peptide used as a substrate for HIV-1 protease. On the basis of sequence homology and molecular modeling, the 106 N-terminal amino acids of HERV-K PR were predicted to comprise a retroviral protease core domain. An 11.6 kDa protein corresponding to this region was expressed and shown to be a fully functional enzyme. The 11.6 kDa domain of HERV-K PR is unusually stable over a wide pH range, exhibits optimal catalytic activity between pH 4.0 and 5.0, and exists as a dimer at pH 7.0 with a Kd of 50 microM. Like HIV-1 PR, the HERV-K PR core domain is activated by high salt concentrations and processes HIV-1 matrix-capsid polyprotein at the authentic HIV-1 PR recognition site. However, both the 18.2 and 11.6 kDa forms of HERV-K PR were highly resistant to a number of clinically useful HIV-1 PR inhibitors, including ritonavir, indinavir, and saquinavir. This raises the possibility that HERV-K PR may complement HIV-1 PR during infection, and could have implications for protease inhibitor therapy and drug resistance.
Towler
E M
EM
Protein Chemistry Laboratory, Structural Biochemistry Program, SAIC Frederick, Maryland 21702, USA. towlere@ncifcrf.gov
Gulnik
S V
SV
Bhat
T N
TN
Xie
D
D
Gustschina
E
E
Sumpter
T R
TR
Robertson
N
N
Jones
C
C
Sauter
M
M
Mueller-Lantzsch
N
N
Debouck
C
C
Erickson
J W
JW
D000595:Amino Acid Sequence; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D002213:Capsid / Q000378:metabolism; D002384:Catalysis; D019281:Dimerization; D020077:Endogenous Retroviruses / Q000201:enzymology*; D004795:Enzyme Stability; D015683:Gene Products, gag / Q000378:metabolism; D015488:HIV Antigens / Q000378:metabolism; D016333:HIV Protease / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011499:Protein Processing, Post-Translational; D013329:Structure-Activity Relationship; D014764:Viral Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus
D015683:Gene Products, gag; D015488:HIV Antigens; D014764:Viral Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus; C054858:p17 protein, Human Immunodeficiency Virus Type 1; D016282:Aspartic Acid Endopeptidases; D016333:HIV Protease