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J Virol. 2014 Jul;88(13):7221-34. doi: 10.1128/JVI.00269-14. Epub 2014 Apr 16.

Liquefaction of semen generates and later degrades a conserved semenogelin peptide that enhances HIV infection.

Author information

1
Gladstone Institute of Virology and Immunology, University of California, San Francisco, California, USA Department of Urology, University of California, San Francisco, California, USA roann@urology.ucsf.edu.
2
Department of Obstetrics, Gynecology & Reproductive Sciences and Sandler-Moore Mass Spectrometry Core Facility, University of California, San Francisco, California, USA.
3
Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany.
4
Gladstone Institute of Virology and Immunology, University of California, San Francisco, California, USA.
5
Gladstone Institute of Cardiovascular Diseases, University of California, San Francisco, California, USA.
6
Lawrence Berkeley National Laboratory, Berkeley, California, USA.
7
Institute of Pharmaceutical Biotechnology, Ulm University, Ulm, Germany.
8
Department of Urology, University of California, San Francisco, California, USA.
9
Gladstone Institute of Cardiovascular Diseases, University of California, San Francisco, California, USA Department of Epidemiology and Biostatistics, Institute for Human Genetics, University of California, San Francisco, California, USA.
10
Gladstone Institute of Virology and Immunology, University of California, San Francisco, California, USA Departments of Medicine and Microbiology and Immunology, University of California, San Francisco, California, USA.

Abstract

Semen enhances HIV infection in vitro, but how long it retains this activity has not been carefully examined. Immediately postejaculation, semen exists as a semisolid coagulum, which then converts to a more liquid form in a process termed liquefaction. We demonstrate that early during liquefaction, semen exhibits maximal HIV-enhancing activity that gradually declines upon further incubation. The decline in HIV-enhancing activity parallels the degradation of peptide fragments derived from the semenogelins (SEMs), the major components of the coagulum that are cleaved in a site-specific and progressive manner upon initiation of liquefaction. Because amyloid fibrils generated from SEM fragments were recently demonstrated to enhance HIV infection, we set out to determine whether any of the liquefaction-generated SEM fragments associate with the presence of HIV-enhancing activity. We identify SEM1 from amino acids 86 to 107 [SEM1(86-107)] to be a short, cationic, amyloidogenic SEM peptide that is generated early in the process of liquefaction but that, conversely, is lost during prolonged liquefaction due to the activity of serine proteases. Synthetic SEM1(86-107) amyloids directly bind HIV-1 virions and are sufficient to enhance HIV infection of permissive cells. Furthermore, endogenous seminal levels of SEM1(86-107) correlate with donor-dependent variations in viral enhancement activity, and antibodies generated against SEM1(86-107) recognize endogenous amyloids in human semen. The amyloidogenic potential of SEM1(86-107) and its virus-enhancing properties are conserved among great apes, suggesting an evolutionarily conserved function. These studies identify SEM1(86-107) to be a key, HIV-enhancing amyloid species in human semen and underscore the dynamic nature of semen's HIV-enhancing activity.

IMPORTANCE:

Semen, the most common vehicle for HIV transmission, enhances HIV infection in vitro, but how long it retains this activity has not been investigated. Semen naturally undergoes physiological changes over time, whereby it converts from a gel-like consistency to a more liquid form. This process, termed liquefaction, is characterized at the molecular level by site-specific and progressive cleavage of SEMs, the major components of the coagulum, by seminal proteases. We demonstrate that the HIV-enhancing activity of semen gradually decreases over the course of extended liquefaction and identify a naturally occurring semenogelin-derived fragment, SEM1(86-107), whose levels correlate with virus-enhancing activity over the course of liquefaction. SEM1(86-107) amyloids are naturally present in semen, and synthetic SEM1(86-107) fibrils bind virions and are sufficient to enhance HIV infection. Therefore, by characterizing dynamic changes in the HIV-enhancing activity of semen during extended liquefaction, we identified SEM1(86-107) to be a key virus-enhancing component of human semen.

PMID:
24741080
PMCID:
PMC4054457
DOI:
10.1128/JVI.00269-14
[Indexed for MEDLINE]
Free PMC Article
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