1
|
Tsurumi S, Watanabe T, Iwaisako Y, Suzuki Y, Nakano T, Fujimuro M. Kaposi's sarcoma-associated herpesvirus ORF17 plays a key role in capsid maturation. Virology 2021; 558:76-85. [PMID: 33735753 DOI: 10.1016/j.virol.2021.02.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2020] [Revised: 02/12/2021] [Accepted: 02/19/2021] [Indexed: 01/04/2023]
Abstract
Kaposi's sarcoma-associated herpesvirus is a human rhadinovirus of the gammaherpesvirus sub-family. Although herpesviruses are well-studied models of capsid formation and its processes, those of KSHV remain unknown. KSHV ORF17 encoding the viral protease precursor (ORF17-prePR) is thought to contribute to capsid formation; however, functional information is largely unknown. Here, we evaluated the role of ORF17 during capsid formation by generating ORF17-deficient and ORF17 protease-dead KSHV. Both mutants showed a decrease in viral production but not DNA replication. ORF17 R-mut, with a point-mutation at the restriction or release site (R-site) by which ORF17-prePR can be functionally cleaved into a protease (ORF17-PR) and an assembly region (ORF17-pAP/-AP), failed to play a role in viral production. Furthermore, wild type KSHV produced a mature capsid, whereas ORF17-deficient and protease-dead KSHV produced a B-capsid, (i.e., a closed body possessing a circular inner structure). Therefore, ORF17 and its protease function are essential for appropriate capsid maturation.
Collapse
Affiliation(s)
- Sayaka Tsurumi
- Department of Cell Biology, Kyoto Pharmaceutical University, 1 Misasagi-Shichono, Yamashina, Kyoto, 607-8412, Japan
| | - Tadashi Watanabe
- Department of Cell Biology, Kyoto Pharmaceutical University, 1 Misasagi-Shichono, Yamashina, Kyoto, 607-8412, Japan; Department of Virology, Graduate School of Medicine, University of the Ryukyus, 207 Uehara, Nishihara, Nakagami, Okinawa, 903-0215, Japan
| | - Yuki Iwaisako
- Department of Cell Biology, Kyoto Pharmaceutical University, 1 Misasagi-Shichono, Yamashina, Kyoto, 607-8412, Japan
| | - Youichi Suzuki
- Department of Microbiology and Infection Control, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan
| | - Takashi Nakano
- Department of Microbiology and Infection Control, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan
| | - Masahiro Fujimuro
- Department of Cell Biology, Kyoto Pharmaceutical University, 1 Misasagi-Shichono, Yamashina, Kyoto, 607-8412, Japan.
| |
Collapse
|
2
|
San Martín C. Virus Maturation. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1215:129-158. [DOI: 10.1007/978-3-030-14741-9_7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
|
3
|
The Apical Region of the Herpes Simplex Virus Major Capsid Protein Promotes Capsid Maturation. J Virol 2018; 92:JVI.00821-18. [PMID: 29976665 DOI: 10.1128/jvi.00821-18] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Accepted: 06/27/2018] [Indexed: 01/12/2023] Open
Abstract
The herpesvirus capsid assembles in the nucleus as an immature procapsid precursor built around viral scaffold proteins. The event that initiates procapsid maturation is unknown, but it is dependent upon activation of the VP24 internal protease. Scaffold cleavage triggers angularization of the shell and its decoration with the VP26 and pUL25 capsid-surface proteins. In both the procapsid and mature angularized capsid, the apical region of the major capsid protein (VP5) is surface exposed. We investigated whether the VP5 apical region contributes to intracellular transport dynamics following entry into primary sensory neurons and also tested the hypothesis that conserved negatively charged amino acids in the apical region contribute to VP26 acquisition. To our surprise, neither hypothesis proved true. Instead, mutation of glutamic acid residues in the apical region delayed viral propagation and induced focal capsid accumulations in nuclei. Examination of capsid morphogenesis based on epitope unmasking, capsid composition, and ultrastructural analysis indicated that these clusters consisted of procapsids. The results demonstrate that, in addition to established events that occur inside the capsid, the exterior capsid shell promotes capsid morphogenesis and maturation.IMPORTANCE Herpesviruses assemble capsids and encapsidate their genomes by a process that is unlike those of other mammalian viruses but is similar to those of some bacteriophage. Many important aspects of herpesvirus morphogenesis remain enigmatic, including how the capsid shell matures into a stable angularized configuration. Capsid maturation is triggered by activation of a protease that cleaves an internal protein scaffold. We report on the fortuitous discovery that a region of the major capsid protein that is exposed on the outer surface of the capsid also contributes to capsid maturation, demonstrating that the morphogenesis of the capsid shell from its procapsid precursor to the mature angularized form is dependent upon internal and external components of the megastructure.
Collapse
|
4
|
Zühlsdorf M, Hinrichs W. Assemblins as maturational proteases in herpesviruses. J Gen Virol 2017; 98:1969-1984. [PMID: 28758622 DOI: 10.1099/jgv.0.000872] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
During assembly of herpesvirus capsids, a protein scaffold self-assembles to ring-like structures forming the scaffold of the spherical procapsids. Proteolytic activity of the herpesvirus maturational protease causes structural changes that result in angularization of the capsids. In those mature icosahedral capsids, the packaging of viral DNA into the capsids can take place. The strictly regulated protease is called assemblin. It is inactive in its monomeric state and activated by dimerization. The structures of the dimeric forms of several assemblins from all herpesvirus subfamilies have been elucidated in the last two decades. They revealed a unique serine-protease fold with a catalytic triad consisting of a serine and two histidines. Inhibitors that disturb dimerization by binding to the dimerization area were found recently. Additionally, the structure of the monomeric form of assemblin from pseudorabies virus and some monomer-like structures of Kaposi's sarcoma-associated herpesvirus assemblin were solved. These findings are the proof-of-principle for the development of new anti-herpesvirus drugs. Therefore, the most important information on this fascinating and unique class of proteases is summarized here.
Collapse
Affiliation(s)
- Martin Zühlsdorf
- Institute of Biochemistry, University of Greifswald, Felix-Hausdorff-Straße 4, 17489 Greifswald, Germany
| | - Winfried Hinrichs
- Institute of Biochemistry, University of Greifswald, Felix-Hausdorff-Straße 4, 17489 Greifswald, Germany
| |
Collapse
|
5
|
Visualizing Herpesvirus Procapsids in Living Cells. J Virol 2016; 90:10182-10192. [PMID: 27581983 DOI: 10.1128/jvi.01437-16] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Accepted: 08/24/2016] [Indexed: 01/16/2023] Open
Abstract
A complete understanding of herpesvirus morphogenesis requires studies of capsid assembly dynamics in living cells. Although fluorescent tags fused to the VP26 and pUL25 capsid proteins are available, neither of these components is present on the initial capsid assembly, the procapsid. To make procapsids accessible to live-cell imaging, we made a series of recombinant pseudorabies viruses that encoded green fluorescent protein (GFP) fused in frame to the internal capsid scaffold and maturation protease. One recombinant, a GFP-VP24 fusion, maintained wild-type propagation kinetics in vitro and approximated wild-type virulence in vivo The fusion also proved to be well tolerated in herpes simplex virus. Viruses encoding GFP-VP24, along with a traditional capsid reporter fusion (pUL25/mCherry), demonstrated that GFP-VP24 was a reliable capsid marker and revealed that the protein remained capsid associated following entry into cells and upon nuclear docking. These dual-fluorescent viruses made possible the discrimination of procapsids during infection and monitoring of capsid shell maturation kinetics. The results demonstrate the feasibility of imaging herpesvirus procapsids and their morphogenesis in living cells and indicate that the encapsidation machinery does not substantially help coordinate capsid shell maturation. IMPORTANCE The family Herpesviridae consists of human and veterinary pathogens that cause a wide range of diseases in their respective hosts. These viruses share structurally related icosahedral capsids that encase the double-stranded DNA (dsDNA) viral genome. The dynamics of capsid assembly and maturation have been inaccessible to examination in living cells. This study has overcome this technical hurdle and provides new insights into this fundamental stage of herpesvirus infection.
Collapse
|
6
|
Zühlsdorf M, Werten S, Klupp BG, Palm GJ, Mettenleiter TC, Hinrichs W. Dimerization-Induced Allosteric Changes of the Oxyanion-Hole Loop Activate the Pseudorabies Virus Assemblin pUL26N, a Herpesvirus Serine Protease. PLoS Pathog 2015; 11:e1005045. [PMID: 26161660 PMCID: PMC4498786 DOI: 10.1371/journal.ppat.1005045] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Accepted: 06/24/2015] [Indexed: 01/01/2023] Open
Abstract
Herpesviruses encode a characteristic serine protease with a unique fold and an active site that comprises the unusual triad Ser-His-His. The protease is essential for viral replication and as such constitutes a promising drug target. In solution, a dynamic equilibrium exists between an inactive monomeric and an active dimeric form of the enzyme, which is believed to play a key regulatory role in the orchestration of proteolysis and capsid assembly. Currently available crystal structures of herpesvirus proteases correspond either to the dimeric state or to complexes with peptide mimetics that alter the dimerization interface. In contrast, the structure of the native monomeric state has remained elusive. Here, we present the three-dimensional structures of native monomeric, active dimeric, and diisopropyl fluorophosphate-inhibited dimeric protease derived from pseudorabies virus, an alphaherpesvirus of swine. These structures, solved by X-ray crystallography to respective resolutions of 2.05, 2.10 and 2.03 Å, allow a direct comparison of the main conformational states of the protease. In the dimeric form, a functional oxyanion hole is formed by a loop of 10 amino-acid residues encompassing two consecutive arginine residues (Arg136 and Arg137); both are strictly conserved throughout the herpesviruses. In the monomeric form, the top of the loop is shifted by approximately 11 Å, resulting in a complete disruption of the oxyanion hole and loss of activity. The dimerization-induced allosteric changes described here form the physical basis for the concentration-dependent activation of the protease, which is essential for proper virus replication. Small-angle X-ray scattering experiments confirmed a concentration-dependent equilibrium of monomeric and dimeric protease in solution. Herpesviruses encode a unique serine protease, which is essential for herpesvirus capsid maturation and is therefore an interesting target for drug development. In solution, this protease exists in an equilibrium of an inactive monomeric and an active dimeric form. All currently available crystal structures of herpesvirus proteases represent complexes, particularly dimers. Here we show the first three-dimensional structure of the native monomeric form in addition to the native and the chemically inactivated dimeric form of the protease derived from the porcine herpesvirus pseudorabies virus. Comparison of the monomeric and dimeric form allows predictions on the structural changes that occur during dimerization and shed light onto the process of protease activation. These new crystal structures provide a rational base to develop drugs preventing dimerization and therefore impeding herpesvirus capsid maturation. Furthermore, it is likely that this mechanism is conserved throughout the herpesviruses.
Collapse
Affiliation(s)
- Martin Zühlsdorf
- Institute of Biochemistry, University of Greifswald, Greifswald, Germany
| | - Sebastiaan Werten
- Institute of Biochemistry, University of Greifswald, Greifswald, Germany
| | - Barbara G. Klupp
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald—Insel Riems, Germany
| | - Gottfried J. Palm
- Institute of Biochemistry, University of Greifswald, Greifswald, Germany
| | - Thomas C. Mettenleiter
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald—Insel Riems, Germany
| | - Winfried Hinrichs
- Institute of Biochemistry, University of Greifswald, Greifswald, Germany
- * E-mail:
| |
Collapse
|
7
|
Mutational analysis of the Pseudomonas aeruginosa myovirus KZ morphogenetic protease gp175. J Virol 2013; 87:8713-25. [PMID: 23740980 DOI: 10.1128/jvi.01008-13] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pseudomonas aeruginosa myovirus KZ has a 270-kb genome within a T=27 icosahedral capsid that contains a large, unusual, and structurally well-defined protein cylindrical inner body (IB) spanning its interior. Proteolysis forms a pivotal stage in KZ head and IB morphogenesis, with the protease gp175 cleaving at least 19 of 49 different head proteins, including the major capsid protein and five major structural IB proteins. Here we show that the purified mature form of gp175 is active and cleaves purified IB structural proteins gp93 and gp89. Expression vector synthesis and purification of the zymogen/precursor yielded an active, mature-length protease, showing independent C-terminal gp175 self-cleavage autoactivation. Mutation of either the predicted catalytic serine or histidine inactivated mature gp175, supporting its classification as a serine protease and representing the first such direct biochemical demonstration with purified protease and substrate proteins for any phage protease. These mutations also blocked self-cleavage of the precursor while allowing intermolecular gp175 processing. To confirm the cleavage specificity of gp175, we mutated three cleavage sites in gp93, which blocked proteolysis at these sites. The N-terminal propeptide of gp93 was shown to undergo more extensive proteolysis than previously identified. We found that proteolysis in gp93 progressed from the N to C terminus, while blocking cleavage sites slowed but did not eliminate downstream proteolysis. These findings were shown by informatics to be relevant to the head morphogenesis of numbers of other related IB-containing giant phages as well as to T4 and herpesviruses, which have homologous proteases.
Collapse
|
8
|
Yang K, Wills EG, Baines JD. Release of the herpes simplex virus 1 protease by self cleavage is required for proper conformation of the portal vertex. Virology 2012; 429:63-73. [PMID: 22543049 DOI: 10.1016/j.virol.2012.03.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2012] [Revised: 02/11/2012] [Accepted: 03/06/2012] [Indexed: 10/28/2022]
Abstract
We identify an NLS within herpes simplex virus scaffold proteins that is required for optimal nuclear import of these proteins into infected or uninfected nuclei, and is sufficient to mediate nuclear import of GFP. A virus lacking this NLS replicated to titers reduced by 1000-fold, but was able to make capsids containing both scaffold and portal proteins suggesting that other functions can complement the NLS in infected cells. We also show that Vp22a, the major scaffold protein, is sufficient to mediate the incorporation of portal protein into capsids, whereas proper portal immunoreactivity in the capsid requires the larger scaffold protein pU(L)26. Finally, capsid angularization in infected cells did not require the HSV-1 protease unless full length pU(L)26 was expressed. These data suggest that the HSV-1 portal undergoes conformational changes during capsid maturation, and reveal that full length pU(L)26 is required for this conformational change.
Collapse
Affiliation(s)
- Kui Yang
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA
| | | | | |
Collapse
|
9
|
Fernandes SM, Brignole EJ, Gibson W. Cytomegalovirus capsid protease: biological substrates are cleaved more efficiently by full-length enzyme (pUL80a) than by the catalytic domain (assemblin). J Virol 2011; 85:3526-34. [PMID: 21270147 PMCID: PMC3067851 DOI: 10.1128/jvi.02663-10] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Accepted: 01/19/2011] [Indexed: 11/20/2022] Open
Abstract
We compared the full-length capsid maturational protease (pPR, pUL80a) of human cytomegalovirus with its proteolytic domain (assemblin) for the ability to cleave two biological substrates, and we found that pPR is more efficient with both. Affinity-purified, refolded enzymes and substrates were combined under defined reaction conditions, and cleavage was monitored and quantified following staining of the resulting electrophoretically separated fragments. The enzymes were stabilized against self-cleavage by a single point mutation in each cleavage site (ICRMT-pPR and IC-assemblin). The substrates were pPR itself, inactivated by replacing its catalytic nucleophile (S132A-pPR), and the sequence-related assembly protein precursor (pAP, pUL80.5). Our results showed that (i) ICRMT-pPR is 5- to 10-fold more efficient than assemblin for all cleavages measured (i.e., the M site of pAP and the M, R, and I sites of S132A-pPR). (ii) Cleavage of substrate S132A-pPR proceeded M>R>I for both enzymes. (iii) Na(2)SO(4) reduced M- and R-site cleavage efficiency by ICRMT-pPR, in contrast to its enhancing effect for both enzymes on I site and small peptide cleavage. (iv) Disrupting oligomerization of either the pPR enzyme or substrate by mutating Leu382 in the amino-conserved domain reduced cleavage efficiency two- to fourfold. (v) Finally, ICRMT-pPR mutants that include the amino-conserved domain, but terminate with Pro481 or Tyr469, retain the enzymatic characteristics that distinguish pPR from assemblin. These findings show that the scaffolding portion of pPR increases its enzymatic activity on biologically relevant protein substrates and provide an additional link between the structure of this essential viral enzyme and its biological mechanism.
Collapse
Affiliation(s)
- Steve M. Fernandes
- Virology Laboratories, Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Maryland 21205
| | - Edward J. Brignole
- Virology Laboratories, Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Maryland 21205
| | - Wade Gibson
- Virology Laboratories, Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Maryland 21205
| |
Collapse
|
10
|
Lazic A, Goetz DH, Nomura AM, Marnett AB, Craik CS. Substrate modulation of enzyme activity in the herpesvirus protease family. J Mol Biol 2007; 373:913-23. [PMID: 17870089 PMCID: PMC2078331 DOI: 10.1016/j.jmb.2007.07.073] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2007] [Revised: 07/21/2007] [Accepted: 07/26/2007] [Indexed: 11/23/2022]
Abstract
The herpesvirus proteases are an example in which allosteric regulation of an enzyme activity is achieved through the formation of quaternary structure. Here, we report a 1.7 A resolution structure of Kaposi's sarcoma-associated herpesvirus protease in complex with a hexapeptide transition state analogue that stabilizes the dimeric state of the enzyme. Extended substrate binding sites are induced upon peptide binding. In particular, 104 A2 of surface are buried in the newly formed S4 pocket when tyrosine binds at this site. The peptide inhibitor also induces a rearrangement of residues that stabilizes the oxyanion hole and the dimer interface. Concomitant with the structural changes, an increase in catalytic efficiency of the enzyme results upon extended substrate binding. A nearly 20-fold increase in kcat/KM results upon extending the peptide substrate from a tetrapeptide to a hexapeptide exclusively due to a KM effect. This suggests that the mechanism by which herpesvirus proteases achieve their high specificity is by using extended substrates to modulate both the structure and activity of the enzyme.
Collapse
Affiliation(s)
- Ana Lazic
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158-2517, USA
| | | | | | | | | |
Collapse
|
11
|
Brignole EJ, Gibson W. Enzymatic activities of human cytomegalovirus maturational protease assemblin and its precursor (pPR, pUL80a) are comparable: [corrected] maximal activity of pPR requires self-interaction through its scaffolding domain. J Virol 2007; 81:4091-103. [PMID: 17287260 PMCID: PMC1866128 DOI: 10.1128/jvi.02821-06] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Herpesviruses encode an essential, maturational serine protease whose catalytic domain, assemblin (28 kDa), is released by self-cleavage from a 74-kDa precursor (pPR, pUL80a). Although there is considerable information about the structure and enzymatic characteristics of assemblin, a potential pharmacologic target, comparatively little is known about these features of the precursor. To begin studying pPR, we introduced five point mutations that stabilize it against self-cleavage at its internal (I), cryptic (C), release (R), and maturational (M) sites and at a newly discovered "tail" (T) site. The resulting mutants, called ICRM-pPR and ICRMT-pPR, were expressed in bacteria, denatured in urea, purified by immobilized metal affinity chromatography, and renatured by a two-step dialysis procedure and by a new method of sedimentation into glycerol gradients. The enzymatic activities of the pPR mutants were indistinguishable from that of IC-assemblin prepared in parallel for comparison, as determined by using a fluorogenic peptide cleavage assay, and approximated rates previously reported for purified assemblin. The percentage of active enzyme in the preparations was also comparable, as determined by using a covalent-binding suicide substrate. An unexpected finding was that, in the absence of the kosmotrope Na2SO4, optimal activity of pPR requires interaction through its scaffolding domain. We conclude that although the enzymatic activities of assemblin and its precursor are comparable, there may be differences in how their catalytic sites become fully activated.
Collapse
Affiliation(s)
- Edward J Brignole
- Virology Laboratories, The Department of Pharmacology & Molecular Sciences, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA.
| | | |
Collapse
|
12
|
Cottier V, Barberis A, Lüthi U. Novel yeast cell-based assay to screen for inhibitors of human cytomegalovirus protease in a high-throughput format. Antimicrob Agents Chemother 2006; 50:565-71. [PMID: 16436711 PMCID: PMC1366920 DOI: 10.1128/aac.50.2.565-571.2006] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The protease encoded by the human cytomegalovirus (HCMV) is an attractive target for antiviral drug development because of its essential function in viral replication. We describe here a cellular assay in the yeast Saccharomyces cerevisiae for the identification of small molecule inhibitors of HCMV protease by conditional growth in selective medium. In this system, the protease cleavage sequence is inserted into the N-(5'-phosphoribosyl)anthranilate isomerase (Trp1p), a yeast protein essential for cell proliferation in the absence of tryptophan. Coexpression of HCMV protease with the engineered Trp1p substrate in yeast cells results in site-specific cleavage and functional inactivation of the Trp1p enzyme, thereby leading to an arrest of cell proliferation. This growth arrest can be suppressed by the addition of validated HCMV protease inhibitors. The growth selection system presented here provides the basis for a high-throughput screen to identify HCMV protease inhibitors that are active in eukaryotic cells.
Collapse
Affiliation(s)
- Valérie Cottier
- ESBATech AG, Wagistr. 21, CH-8952 Zurich-Schlieren, Switzerland
| | | | | |
Collapse
|
13
|
McCartney SA, Brignole EJ, Kolegraff KN, Loveland AN, Ussin LM, Gibson W. Chemical Rescue of I-site Cleavage in Living Cells and in Vitro Discriminates between the Cytomegalovirus Protease, Assemblin, and Its Precursor, pUL80a. J Biol Chem 2005; 280:33206-12. [PMID: 16036911 DOI: 10.1074/jbc.m506876200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Chemical rescue is an established approach that offers a directed strategy for designing mutant enzymes in which activity can be restored by supplying an appropriate exogenous compound. This method has been used successfully to study a broad range of enzymes in vitro, but its application to living systems has received less attention. We have investigated the feasibility of using chemical rescue to make a conditional-lethal mutant of the cytomegalovirus (CMV) maturational protease. The 28-kDa CMV serine protease, assemblin, has a Ser-His-His catalytic triad and an internal (I) cleavage site near its midpoint. We found that imidazole can restore I-site cleavage to mutants inactivated by replacing the critical active site His with Ala or with Gly, which rescued better. Comparable rescue was observed for counterpart mutants of the human and simian CMV assemblin homologs and occurred in both living cells and in vitro. Cleavage was established to be at the correct site by amino acid sequencing and proceeded at approximately 11%/h in bacteria and approximately 30%/h in vitro. The same mutations were unresponsive to chemical rescue in the context of the assemblin precursor, pUL80a. This catalytic difference distinguishes the two forms of the CMV protease.
Collapse
Affiliation(s)
- Stephen A McCartney
- Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | | | | | | | | | | |
Collapse
|
14
|
Buisson M, Hernandez JF, Lascoux D, Schoehn G, Forest E, Arlaud G, Seigneurin JM, Ruigrok RWH, Burmeister WP. The crystal structure of the Epstein-Barr virus protease shows rearrangement of the processed C terminus. J Mol Biol 2002; 324:89-103. [PMID: 12421561 DOI: 10.1016/s0022-2836(02)01040-9] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Epstein-Barr virus (EBV) belongs to the gamma-herpesvirinae subfamily of the Herpesviridae. The protease domain of the assemblin protein of herpesviruses forms a monomer-dimer equilibrium in solution. The protease domain of EBV was expressed in Escherichia coli and its structure was solved by X-ray crystallography to 2.3A resolution after inhibition with diisopropyl-fluorophosphate (DFP). The overall structure confirms the conservation of the homodimer and its structure throughout the alpha, beta, and gamma-herpesvirinae. The substrate recognition could be modelled using information from the DFP binding, from a crystal contact, suggesting that the substrate forms an antiparallel beta-strand extending strand beta5, and from the comparison with the structure of a peptidomimetic inhibitor bound to cytomegalovirus protease. The long insert between beta-strands 1 and 2, which was disordered in the KSHV protease structure, was found to be ordered in the EBV protease and shows the same conformation as observed for proteases in the alpha and beta-herpesvirus families. In contrast to previous structures, the long loop located between beta-strands 5 and 6 is partially ordered, probably due to DFP inhibition and a crystal contact. It also contributes to substrate recognition. The protease shows a specific recognition of its own C terminus in a binding pocket involving residue Phe210 of the other monomer interacting across the dimer interface. This suggests conformational changes of the protease domain after its release from the assemblin precursor followed by burial of the new C terminus and a possible effect onto the monomer-dimer equilibrium. The importance of the processed C terminus was confirmed using a mutant protease carrying a C-terminal extension and a mutated release site, which shows different solution properties and a strongly reduced enzymatic activity.
Collapse
Affiliation(s)
- Marlyse Buisson
- Laboratoire de Virologie, Hôpital Michallon, BP 217, 38043 Grenoble Cedex 9, France
| | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Wittwer AJ, Funckes-Shippy CL, Hippenmeyer PJ. Recombinant full-length human cytomegalovirus protease has lower activity than recombinant processed protease domain in purified enzyme and cell-based assays. Antiviral Res 2002; 55:291-306. [PMID: 12103430 DOI: 10.1016/s0166-3542(02)00051-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Herpesviruses encode a protease that is essential for virus replication. The protease undergoes cleavage to a processed form during capsid maturation. A recombinant 75 kDa form of the protease from human cytomegalovirus was purified and compared with the recombinant 29 kDa processed form. Modification with an active site titrant suggested that most of each recombinant protease preparation was active (66 and 86%, respectively). Protease activity was compared using a low-molecular weight peptide substrate and the native substrate, capsid assembly protein. In addition, a cell-based assay for both enzymes was developed in which the target sequence of the protease has been fused inframe into the herpes simplex virus VP16 molecule. Cleavage of the fusion protein by the protease releases the carboxyl terminal transactivation domain, resulting in a decrease in the ability of the fusion molecule to transactivate a target promoter linked to a reporter gene in mammalian cells. Results suggest that the 75 kDa form of the enzyme is significantly less active than the 29 kDa form by all criteria.
Collapse
Affiliation(s)
- Arthur J Wittwer
- Pharmacia Discovery Research, 700 Chesterfield Village Parkway North, St. Louis, MO 63198, USA
| | | | | |
Collapse
|
16
|
Sheaffer AK, Newcomb WW, Gao M, Yu D, Weller SK, Brown JC, Tenney DJ. Herpes simplex virus DNA cleavage and packaging proteins associate with the procapsid prior to its maturation. J Virol 2001; 75:687-98. [PMID: 11134282 PMCID: PMC113965 DOI: 10.1128/jvi.75.2.687-698.2001] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Packaging of DNA into preformed capsids is a fundamental early event in the assembly of herpes simplex virus type 1 (HSV-1) virions. Replicated viral DNA genomes, in the form of complex branched concatemers, and unstable spherical precursor capsids termed procapsids are thought to be the substrates for the DNA-packaging reaction. In addition, seven viral proteins are required for packaging, although their individual functions are undefined. By analogy to well-characterized bacteriophage systems, the association of these proteins with various forms of capsids, including procapsids, might be expected to clarify their roles in the packaging process. While the HSV-1 UL6, UL15, UL25, and UL28 packaging proteins are known to associate with different forms of stable capsids, their association with procapsids has not been tested. Therefore, we isolated HSV-1 procapsids from infected cells and used Western blotting to identify the packaging proteins present. Procapsids contained UL15 and UL28 proteins; the levels of both proteins are diminished in more mature DNA-containing C-capsids. In contrast, UL6 protein levels were approximately the same in procapsids, B-capsids, and C-capsids. The amount of UL25 protein was reduced in procapsids relative to that in more mature B-capsids. Moreover, C-capsids contained the highest level of UL25 protein, 15-fold higher than that in procapsids. Our results support current hypotheses on HSV DNA packaging: (i) transient association of UL15 and UL28 proteins with maturing capsids is consistent with their proposed involvement in site-specific cleavage of the viral DNA (terminase activity); (ii) the UL6 protein may be an integral component of the capsid shell; and (iii) the UL25 protein may associate with capsids after scaffold loss and DNA packaging, sealing the DNA within capsids.
Collapse
Affiliation(s)
- A K Sheaffer
- Bristol-Myers Squibb Pharmaceutical Research Institute, Wallingford, Connecticut 06492, USA
| | | | | | | | | | | | | |
Collapse
|
17
|
Warner SC, Desai P, Person S. Second-site mutations encoding residues 34 and 78 of the major capsid protein (VP5) of herpes simplex virus type 1 are important for overcoming a blocked maturation cleavage site of the capsid scaffold proteins. Virology 2000; 278:217-26. [PMID: 11112496 DOI: 10.1006/viro.2000.0657] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
During assembly of the herpes simplex type 1 capsid, the major capsid protein VP5 interacts with the C-terminal residues of the scaffold proteins encoded by UL26 and UL26.5. Subsequent to capsid assembly the scaffold proteins are cleaved at the maturation site by a serine protease also encoded by UL26, thereby enabling the bulk of the scaffold proteins to be released from the capsid. Previously, a mutant virus (KUL26-610/611) was isolated in which this maturation cleavage site was blocked by replacing the Ala/Ser at the 610/611 cleavage site by Glu/Phe. This mutation was lethal and required a transformed cell line expressing wild-type UL26 gene products for growth. Although the mutation was lethal, spontaneous reversions occurred at a high frequency. Previously, a small number of revertants were isolated and all were found to have second-site mutations in VP5. The purpose of the present study was to do a comprehensive determination of the sites altered in VP5 by the second-site mutations. To do this, an additional 25 independent spontaneous revertants were characterized. Seven of the 25 arose by GC --> GT changes in codon 78, giving rise to an alanine to valine substitution. Four were the result of base changes at codon 34 but two different amino acids were produced as the changes were at different positions in the codon. Two mutations were detected at position 41 and mutations that occurred once were found at codons 69 and 80. Thus, 15 of the 25 second-site mutants were localized to codons 34 to 80 of VP5, which contains 1374 amino acids. The remaining 10 revertants had codon changes at nine different sites, of which the most N-terminal was altered at codon 187 and the most C-terminal at codon 1317. As noted in the much smaller study a preponderance of the second-site mutants in VP5 were altered in codons at the extreme N-terminus of VP5. It is especially noteworthy that 11 out of 25 of the mutations occurred at codons 34 and 78. As expected, all of the revertants isolated were shown to retain the original KUL26-610/611 mutation, and the scaffold proteins remain uncleaved. All showed decreased retention of VP24 in the B capsids compared to the wild-type KOS, but more than the KUL26-610/611 parental virus. The revertants all had decreased growth rates of 2 to 18% compared to that of KOS and showed varying degrees of sensitivity when grown at 39.5 degrees C. The mutations in VP5 of three of the previously isolated viruses (PR5, PR6, and PR7) were transferred into a wild-type background, i.e., a virus encoding wild-type UL26 and UL26.5 gene products. All replicated in nonpermissive (Vero) cells and cleaved scaffold proteins. PR5 and PR6 in the wild-type background gave wild-type burst sizes and gave C-capsids that retained VP24 at approximately wild-type levels. The third revertant, PR7, in the wild-type background showed only a twofold increase of burst size (to 20% of wild-type) and the capsids showed little or no increase of VP24 retention. Therefore, the second-site mutations of PR7 (R69C) by itself had a negative effect on virus replication. By contrast the temperature sensitivity of PR6 and PR7 remained unchanged in the wild-type background. Thus the temperature sensitivity of PR6 and PR7 resides in VP5 independently of the mutation in the UL26 cleavage site.
Collapse
Affiliation(s)
- S C Warner
- Virology Laboratories, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2185, USA
| | | | | |
Collapse
|
18
|
Sheaffer AK, Newcomb WW, Brown JC, Gao M, Weller SK, Tenney DJ. Evidence for controlled incorporation of herpes simplex virus type 1 UL26 protease into capsids. J Virol 2000; 74:6838-48. [PMID: 10888623 PMCID: PMC112201 DOI: 10.1128/jvi.74.15.6838-6848.2000] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Herpes simplex virus type 1 (HSV-1) capsids are initially assembled with an internal protein scaffold. The scaffold proteins, encoded by overlapping in-frame UL26 and UL26.5 transcripts, are essential for formation and efficient maturation of capsids. UL26 encodes an N-terminal protease domain, and its C-terminal oligomerization and capsid protein-binding domains are identical to those of UL26.5. The UL26 protease cleaves itself, releasing minor scaffold proteins VP24 and VP21, and the more abundant UL26.5 protein, releasing the major scaffold protein VP22a. Unlike VP21 and VP22a, which are removed from capsids upon DNA packaging, we demonstrate that VP24 (containing the protease domain) is quantitatively retained. To investigate factors controlling UL26 capsid incorporation and retention, we used a mutant virus that fails to express UL26.5 (DeltaICP35 virus). Purified DeltaICP35 B capsids showed altered sucrose gradient sedimentation and lacked the dense scaffold core seen in micrographs of wild-type B capsids but contained capsid shell proteins in wild-type amounts. Despite C-terminal sequence identity between UL26 and UL26.5, DeltaICP35 capsids lacking UL26.5 products did not contain compensatory high levels of UL26 proteins. Therefore, HSV capsids can be maintained and/or assembled on a minimal scaffold containing only wild-type levels of UL26 proteins. In contrast to UL26.5, increased expression of UL26 did not compensate for the DeltaICP35 growth defect. While indirect, these findings are consistent with the view that UL26 products are restricted from occupying abundant UL26.5 binding sites within the capsid and that this restriction is not controlled by the level of UL26 protein expression. Additionally, DeltaICP35 capsids contained an altered complement of DNA cleavage and packaging proteins, suggesting a previously unrecognized role for the scaffold in this process.
Collapse
Affiliation(s)
- A K Sheaffer
- Department of Virology, Bristol-Myers Squibb Pharmaceutical Research Institute, Wallingford, Connecticut 06492, USA
| | | | | | | | | | | |
Collapse
|
19
|
Abstract
Viruses of the family Herpesviridae are responsible for a diverse set of human diseases. The available treatments are largely ineffective, with the exception of a few drugs for treatment of herpes simplex virus (HSV) infections. For several members of this DNA virus family, advances have been made recently in the biochemistry and structural biology of the essential viral protease, revealing common features that may be possible to exploit in the development of a new class of anti-herpesvirus agents. The herpesvirus proteases have been identified as belonging to a unique class of serine protease, with a Ser-His-His catalytic triad. A new, single domain protein fold has been determined by X-ray crystallography for the proteases of at least three different herpesviruses. Also unique for serine proteases, dimerization has been shown to be required for activity of the cytomegalovirus and HSV proteases. The dimerization requirement seriously impacts methods needed for productive, functional analysis and inhibitor discovery. The conserved functional and catalytic properties of the herpesvirus proteases lead to common considerations for this group of proteases in the early phases of inhibitor discovery. In general, classical serine protease inhibitors that react with active site residues do not readily inactivate the herpesvirus proteases. There has been progress however, with activated carbonyls that exploit the selective nucleophilicity of the active site serine. In addition, screening of chemical libraries has yielded novel structures as starting points for drug development. Recent crystal structures of the herpesvirus proteases now allow more direct interpretation of ligand structure-activity relationships. This review first describes basic functional aspects of herpesvirus protease biology and enzymology. Then we discuss inhibitors identified to date and the prospects for their future development.
Collapse
Affiliation(s)
- L Waxman
- Department of Antiviral Research, Merck Research Laboratories, West Point, PA 19486, USA
| | | |
Collapse
|
20
|
Abstract
During herpes simplex virus (HSV) assembly, immature procapsids must expel their internal scaffold proteins, transform their outer shell to form mature polyhedrons, and become packaged with the viral double-stranded (ds) DNA genome. A large number of virally encoded proteins are required for successful completion of these events, but their molecular roles are poorly understood. By analogy with the dsDNA bacteriophage we reasoned that HSV DNA packaging might be an ATP-requiring process and tested this hypothesis by adding an ATP depletion cocktail to cells accumulating unpackaged procapsids due to the presence of a temperature-sensitive lesion in the HSV maturational protease UL26. Following return to permissive temperature, HSV capsids were found to be unable to package DNA, suggesting that this process is indeed ATP dependent. Surprisingly, however, the display of epitopes indicative of capsid maturation was also inhibited. We conclude that either formation of these epitopes directly requires ATP or capsid maturation is normally arrested by a proofreading mechanism until DNA packaging has been successfully completed.
Collapse
Affiliation(s)
- A Dasgupta
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | | |
Collapse
|
21
|
Person S, Desai P. Capsids are formed in a mutant virus blocked at the maturation site of the UL26 and UL26.5 open reading frames of herpes simplex virus type 1 but are not formed in a null mutant of UL38 (VP19C). Virology 1998; 242:193-203. [PMID: 9501049 DOI: 10.1006/viro.1997.9005] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previously we reported that null mutant viruses of UL19 (VP5) or of UL18 (VP23), essential components of herpes simplex virus type 1 (HSV-1) capsid shells, do not form precursor capsid structures as judged by sedimentation and electron microscope analysis. A goal of the present experiments was to isolate a null mutant virus for the remaining essential component of capsid shells, VP19C, encoded by the UL38 open reading frame (ORF). Furthermore, we wished to determine if a virus altered in the UL26 maturation cleavage site at residues 610 and 611 produced a lethal phenotype. Therefore, we decided to isolate cell lines that encode and express multiple capsid genes. Several cell lines were isolated by transformation of Vero cells and one designated C32 expressed all of the essential capsid proteins. Using this cell line we isolated a null mutant virus in the UL38 ORF and a mutant virus that was altered at residues 610 and 611 of the UL26 and UL26.5 gene products. We found that the null mutant in VP19C did not form a detectable product as judged by sedimentation and electron microscope analyses following infection of nonpermissive cells. The mutant virus altered at the UL26 maturation site resulted in the accumulation of B capsids. Therefore, cleavage at this site was essential for the maturation of B capsids into C capsids. Interestingly, the absence of cleavage at the maturation site was required for the retention of VP24 in the capsid.
Collapse
Affiliation(s)
- S Person
- Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | | |
Collapse
|
22
|
Flynn DL, Abood NA, Holwerda BC. Recent advances in antiviral research: identification of inhibitors of the herpesvirus proteases. Curr Opin Chem Biol 1997; 1:190-6. [PMID: 9667847 DOI: 10.1016/s1367-5931(97)80009-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Major advances have been reported in the last two years regarding the molecular biology and structural properties of the herpesvirus proteases. X-ray diffraction studies have enabled several groups to solve the structure of the human cytomegalovirus protease. Fluorescence-based substrate assays have also been recently reported. These substrates exhibit sufficient kinetic and sensitivity properties to enable high-throughput screening efforts dedicated toward the discovery of protease inhibitors. Three classes of inhibitors have been reported recently: nonpeptidic aryl trifluoromethylketones; alternate substrate inhibitors (benzoxazinones/azalactones); and thiol-modifying inhibitors. The thiol-modifying class offers a unique opportunity to discover inhibitors specific to the human cytomegalovirus protease, as this protease requires reduced cysteine residues for its enzymatic activity.
Collapse
Affiliation(s)
- D L Flynn
- Searle Research and Development, Department of Medicinal Chemistry, 800 N Lindbergh Blvd, St Louis, MO 63167, USA.
| | | | | |
Collapse
|
23
|
Abstract
Herpesvirus proteases have emerged as targets for the development of novel antiviral drugs. These enzymes, which are necessary for the replication of all herpesviruses, are serine proteases, but possess a unique structure as revealed by solution of the crystal structure of human cytomegalovirus protease. Many of the biochemical properties of these enzymes are now explained by the structure. Conventional serine protease inhibitors are not potent inhibitors of these enzymes and therefore the search for potent inhibitors possessing necessary features of an effective antiviral will require novel approaches. The three-dimensional structure serves as a milestone for continued endeavors towards this goal.
Collapse
Affiliation(s)
- B C Holwerda
- Searle Research and Development, St. Louis, MO 63198, USA.
| |
Collapse
|
24
|
Robertson BJ, McCann PJ, Matusick-Kumar L, Preston VG, Gao M. Na, an autoproteolytic product of the herpes simplex virus type 1 protease, can functionally substitute for the assembly protein ICP35. J Virol 1997; 71:1683-7. [PMID: 8995700 PMCID: PMC191231 DOI: 10.1128/jvi.71.2.1683-1687.1997] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The herpes simplex virus type 1 (HSV-1) protease and its substrate, the assembly protein ICP35, are involved in virion maturation. Both proteins are encoded by a single open reading frame but are translated independently from 3'-coterminal mRNAs of different sizes and are in frame. The herpesvirus shell assembles around an internal scaffold which is subsequently lost during packaging of the viral genome. The scaffold is composed of ICP35, which is the major component, and autoproteolytically processed forms of the viral protease containing sequences common to ICP35 (Nb). In the baculovirus system, HSV-1 intact capsids can be formed in the presence of the protease or ICP35, indicating that the protease may substitute for ICP35 (Thomsen et al., J. Virol. 68:2442-2457, 1994). This is further supported by the fact that ICP35, in contrast to the protease, is not absolutely essential for viral growth. The processed intermediate of the protease analogous to ICP35 is the 388-amino-acid (aa) protein, Na, which is an N-terminal 59-aa extension of the 329-aa ICP35. To directly examine whether Na can functionally substitute for ICP35 during viral replication, we first constructed a mutant virus, Na delta35, in which 35 aa from the N terminus of Na were deleted. Phenotypic analysis of the mutant showed that this deletion had no effect on protease function. The function of Na was further examined by construction of a plasmid expressing Na alone and testing its ability to complement the growth of the mutant Prb virus in the absence of ICP35. Our results demonstrate that Na can functionally substitute for ICP35 during viral replication.
Collapse
Affiliation(s)
- B J Robertson
- Department of Virology, Bristol-Myers Squibb Pharmaceutical Research Institute, Wallingford, Connecticut 06492-7660, USA
| | | | | | | | | |
Collapse
|
25
|
Wood LJ, Baxter MK, Plafker SM, Gibson W. Human cytomegalovirus capsid assembly protein precursor (pUL80.5) interacts with itself and with the major capsid protein (pUL86) through two different domains. J Virol 1997; 71:179-90. [PMID: 8985337 PMCID: PMC191038 DOI: 10.1128/jvi.71.1.179-190.1997] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We have used the yeast GAL4 two-hybrid system to examine interactions between the human cytomegalovirus (HCMV) major capsid protein (MCP, encoded by UL86) and the precursor assembly protein (pAP, encoded by UL80.5 and cleaved at its carboxyl end to yield AP) and found that (i) the pAP interacts with the MCP through residues located within the carboxy-terminal 21 amino acids of the pAP, called the carboxyl conserved domain (CCD); (ii) the pAP interacts with itself through a separate region, called the amino conserved domain (ACD), located between amino acids His34 and Arg52 near the amino end of the molecule; (iii) the simian CMV (SCMV) pAP and AP can interact with or replace their HCMV counterparts in these interactions, whereas the herpes simplex virus pAP and AP homologs cannot; and (iv) the HCMV and SCMV maturational proteinase precursors (ACpra, encoded by UL80a and APNG1, respectively) can interact with the pAP and MCP. The ACD and CCD amino acid sequences are highly conserved among members of the betaherpesvirus group and appear to have counterparts in the alpha- and gammaherpesvirus pAP homologs. Deleting the ACD from the HCMV pAP, or substituting Ala for a conserved Leu in the ACD, eliminated detectable pAP self-interaction and also substantially reduced MCP binding in the two-hybrid assay. This finding indicates that the pAP self-interaction influences the pAP-MCP interaction. Immunofluorescence studies corroborated the pAP-MCP interaction detected in the GAL4 two-hybrid experiments and showed that nuclear transport of the MCP was mediated by pAP but not AP. We conclude that the pAP interacts with the MCP, that this interaction is mediated by the CCD and is influenced by pAP self-interaction, and that one function of the pAP-MCP interaction may be to provide a controlled mechanism for transporting the MCP into the nucleus.
Collapse
Affiliation(s)
- L J Wood
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | | | | | | |
Collapse
|
26
|
Beaudet-Miller M, Zhang R, Durkin J, Gibson W, Kwong AD, Hong Z. Virus-specific interaction between the human cytomegalovirus major capsid protein and the C terminus of the assembly protein precursor. J Virol 1996; 70:8081-8. [PMID: 8892933 PMCID: PMC190882 DOI: 10.1128/jvi.70.11.8081-8088.1996] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
We previously identified a minimal 12-amino-acid domain in the C terminus of the herpes simplex virus type 1 (HSV-1) scaffolding protein which is required for interaction with the HSV-1 major capsid protein. An alpha-helical structure which maximizes the hydropathicity of the minimal domain is required for the interaction. To address whether cytomegalovirus (CMV) utilizes the same strategy for capsid assembly, several glutathione S-transferase fusion proteins to the C terminus of the CMV assembly protein precursor were produced and purified from bacterial cells. The study showed that the glutathione S-transferase fusion containing 16 amino acids near the C-terminal end was sufficient to interact with the major capsid protein. Interestingly, no cross-interaction between HSV-1 and CMV could be detected. Mutation analysis revealed that a three-amino-acid region at the N-terminal side of the central Phe residue of the CMV interaction domain played a role in determining the viral specificity of the interaction. When this region was converted so as to correspond to that of HSV-1, the CMV assembly protein domain lost its ability to interact with the CMV major capsid protein but gained full interaction with the HSV-1 major capsid protein. To address whether the minimal interaction domain of the CMV assembly protein forms an alpha-helical structure similar to that in HSV-1, peptide competition experiments were carried out. The results showed that a cyclic peptide derived from the interaction domain with a constrained (alpha-helical structure competed for interaction with the major capsid protein much more efficiently than the unconstrained linear peptide. In contrast, a cyclic peptide containing an Ala substitution for the critical Phe residue did not compete for the interaction at all. The results of this study suggest that (i) CMV may have developed a strategy similar to that of HSV-1 for capsid assembly; (ii) the minimal interaction motif in the CMV assembly protein requires an alpha-helix for efficient interaction with the major capsid protein; and (iii) the Phe residue in the CMV minimal interaction domain is critical for interaction with the major capsid protein.
Collapse
Affiliation(s)
- M Beaudet-Miller
- Antiviral Chemotherapy, Schering-Plough Research Institute, Kenilworth, New Jersey 07033-0539, USA
| | | | | | | | | | | |
Collapse
|