ABSTRACT
The nucleocapsid (NC) protein of HIV, which contains two CCHC-type zinc fingers connected by a linker, is a multifunctional protein involved in many of the critical steps of the HIV life cycle. HIV-1 and HIV-2 contain NC proteins NCp7 and NCp8, respectively. The amino acid sequences of both NC proteins are 67% identical. For NCp7, the important elements for RNA binding were found to be the first zinc finger flanked by the linker, as the minimal active domain, and the 3(10) helix in the N-terminus, as the secondary active domain. However, for the NCp8 counterpart in HIV-2, the mechanism for binding to viral RNA has not yet been clarified. In this study, we determined NCp8's three-dimensional structure for the first time and examined the dynamic behavior and chemical shift perturbation as a function of the concentration of viral RNA SL3. Moreover, the specific binding activities of NCp8 and the NCp8-derived peptides with SL3 were examined by a native polyacrylamide gel electrophoresis assay. These results indicate that the RNA recognition mechanism for NCp8 is different from that of NCp7 and that the hydrophobic cleft in the second zinc finger acts as a secondary active domain instead of the 3(10) helix in NCp7. Furthermore, the flexibility of the linker is limited by the hydrogen bond between the first zinc finger (Asn11) and the linker (Arg27), which makes it possible for the sites around Trp10 in the minimal active domain and the secondary active domain to form the binding surface.
Subject(s)
HIV-1/metabolism , RNA/chemistry , gag Gene Products, Human Immunodeficiency Virus/chemistry , gag Gene Products, Human Immunodeficiency Virus/physiology , Binding Sites , Capsid/chemistry , Hydrogen Bonding , Kinetics , Magnetic Resonance Spectroscopy , Models, Chemical , Molecular Conformation , Protein Binding , Protein Structure, Tertiary , Viral Proteins/chemistry , Zinc FingersABSTRACT
Nucleocapsid protein of HIV, containing two CCHC-type zinc fingers connected by a linker, is a multi-functional protein involved in many critical steps of the HIV life cycle. Several in vitro investigations demonstrated that the reactivities of the first zinc finger flanked by the linker of HIV-1 NCp7 and HIV-2 NCp8 were essential for binding to viral RNA, however, that of the second zinc finger flanked by the linker of NCp7 was very weak and non-specific, whereas the part of NCp8 called NCp8-f2, interacted strongly and specifically with viral RNA. In this study, the three-dimensional structure of NCp8-f2 was determined for the first time. Furthermore, we established that NCp8-f2 specifically binds to the stem-loop SD in viral RNA, and that the hydrophobic cleft and the basic residues close to the cleft were essential for specific binding to SD. We discuss the functional significance of NCp8-f2 for NCp8 being a multi-functional protein.
Subject(s)
Capsid Proteins/chemistry , Capsid Proteins/physiology , RNA-Binding Proteins/chemistry , RNA-Binding Proteins/physiology , Amino Acid Sequence , Binding Sites , Magnetic Resonance Spectroscopy , Molecular Conformation , Molecular Sequence Data , Nucleic Acid Conformation , Peptides/chemistry , Protein Binding , Protein Conformation , Protein Structure, Tertiary , RNA/chemistry , Sequence Homology, Amino Acid , Structure-Activity Relationship , Zinc FingersABSTRACT
NCp8 of HIV-2 contains two CCHC-type zinc fingers connected by a linker, and is involved in many critical steps of the virus life cycle. It was previously shown that the first zinc finger flanked by the linker is the minimal active domain for specific binding to viral RNA. In our previous study, we determined the three-dimensional structure of NCp8-f1, including the minimal active domain, and found that a hydrogen bond between Asn(11) N(delta)H and Arg(27) O stabilized the conformation of the linker in the vicinity of the zinc finger [Kodera et al. (1998) Biochemistry 37, 17704-17713]. In this study, RNA binding activities of NCp8-f1 and three types of its mutant peptides were analysed by native PAGE assay. The activity and three-dimensional structure of NCp8-f1/N11A, in which alanine is substituted for Asn(11) thereby affecting the conformation of the linker, was analyzed and compared with those of NCp8-f1. We demonstrated that the existence of Arg(4) and/or Lys(5) and Arg(26) and/or Arg(27) were necessary for binding RNA. Furthermore, the linker's flexible orientation, which is controlled by the hydrogen bond between Asn(11) N(delta)H and Arg(27) O, appears to be a structural basis for NCp8 existing as a multi-functional protein.
