Advances in electron microscopy reveal secrets of HIV and other viruses

November 17, 2014

UC Davis researchers are getting a new look at the workings of HIV and other viruses thanks to new techniques in electron microscopy developed on campus.

The envelope (or Env) protein of HIV is a key target for vaccine makers: it is a key component in RV144, an experimental vaccine that is so far the only candidate to show promise in clinical trials. Also called gp120, the Env protein associates with another protein called gp41 and three gp120/gp41 units associate to form the final trimeric structure. The gp120 trimer is the machine that allows HIV to enter and attack host cells.

Professor R. Holland Cheng's laboratory at UC Davis has previously shown how the gp120 trimer can change its conformation like an opening flower. The new study, published in Nature Scientific Reports Nov. 14, shows that a variable loop, V2, is located at the bottom of the trimer where it helps to hold gp41 in place -- and not at the top of the structure, as previously thought.

"This challenges the existing dogma concerning the architecture of HIV Env immunogen," Cheng said.

Making a vaccine against HIV has always been difficult, at least partly because the proteins on the surface of the virus change so rapidly. Better understanding the structure of the gp120/Env trimer could help in finding less-variable areas of these proteins, not usually exposed to the immune system, which might be targets for a vaccine.

Understanding viral entry

A second pair of back-to-back papers from Cheng's lab uses new techniques in electron microscopy to probe how some common viruses hijack normal cellular processes to enter cells.

Cheng's lab has pioneered techniques in cryoelectron microscopy. Traditionally electron microscopy has relied on coating or impregnating samples with heavy metal elements. Cryoelectron microscopy uses extremely low temperatures to freeze biological structures in place instead.

By taking multiple images from slightly different angles and reconstructing them with computers, Cheng has been able to produce three-dimensional images of viruses and virus proteins and particularly, virus-infected cells.

However, because of the way electrons are scattered from samples, cryoelectron microscopes can only use a limited range of angles, creating a "missing wedge" in imaging infected cells. In one of the papers recently published in the journal PLOS ONE, Lassi Paavolainen and colleagues present a new statistical technique to reconstruct this missing data with no prior knowledge of the sample.

In the companion paper, Pan Soonsawad and colleagues applied the new technique to study the vesicles, or small bubbles that form inside cells when a picornavirus enters. The picornaviruses are a large group that includes the viruses that cause colds, gut infections, polio, hepatitis A and the recent outbreaks of contagious hand-foot-mouth disease (HFMD) spread in infants and children of younger age in U.S. this summer.

Picornaviruses get into cells by getting themselves dragged into an endosome, or pouched-off bubble from the cell's surface inside the cell. Then they exit the endosome and replicate their genetic material, RNA, in the cytoplasm of the host cells.

The new work shows that the endosomes are lined with host proteins called integrins, which are found in cell membranes. When integrins come close together in a membrane, they send signals into the cell. Viruses take advantage of this behavior, Cheng said. Attaching itself to a cell, the virus gathers integrins towards itself, triggering formation of an endosome.

"This virus collects integrins into a pattern so it can be 'swallowed' by the host cells," Cheng said.

Once inside, the new images show the endosomes breaking up as the viruses release their genetic material into the cell, leading to massive virus replication.

Despite the illness they cause, Cheng finds the viruses have their own charm.

"The virus is beautiful, because it has its own geometry that can be reused and redesigned for the benefit of human being," he said.

Indeed, Cheng's laboratory has patented technology that makes use of self-assembling proteins from the coat of Hepatitis E virus, including using them to deliver drugs or vaccines or to target breast cancer.
-end-
Coauthors on the Nature Scientific Reports paper were Carlos G. Moscoso, Li Xing, Jinwen Hui, Jeffrey Hu, Mohammad Baikoghli Kalkhoran, Onur M. Yenigun at UC Davis; Yide Sun, Carlo Zambonelli, Susan W. Barnett, and Indresh K. Srivastava at Novartis Vaccines and Diagnostics Inc., Cambridge, Mass.; Loïc Martin, Commissariat à l'énergie atomique et aux énergies alternatives, Gif-sur-Yvette, France; Lassi Paavolainen and Anders Vahlne, Karolinska Institute, Stockholm, Sweden.

The PLOS ONE papers include coauthors from University of Jyvaskyla, Finland; Tampere University of Technology, Tampere, Finland; and Mahidol University, Bangkok, Thailand.

University of California - Davis

Related HIV Articles from Brightsurf:

BEAT-HIV Delaney collaboratory issues recommendations measuring persistent HIV reservoirs
Spearheaded by Wistar scientists, top worldwide HIV researchers from the BEAT-HIV Martin Delaney Collaboratory to Cure HIV-1 Infection by Combination Immunotherapy (BEAT-HIV Collaboratory) compiled the first comprehensive set of recommendations on how to best measure the size of persistent HIV reservoirs during cure-directed clinical studies.

The Lancet HIV: Study suggests a second patient has been cured of HIV
A study of the second HIV patient to undergo successful stem cell transplantation from donors with a HIV-resistant gene, finds that there was no active viral infection in the patient's blood 30 months after they stopped anti-retroviral therapy, according to a case report published in The Lancet HIV journal and presented at CROI (Conference on Retroviruses and Opportunistic Infections).

Children with HIV score below HIV-negative peers in cognitive, motor function tests
Children who acquired HIV in utero or during birth or breastfeeding did not perform as well as their peers who do not have HIV on tests measuring cognitive ability, motor function and attention, according to a report published online today in Clinical Infectious Diseases.

Efforts to end the HIV epidemic must not ignore people already living with HIV
Efforts to prevent new HIV transmissions in the US must be accompanied by addressing HIV-associated comorbidities to improve the health of people already living with HIV, NIH experts assert in the third of a series of JAMA commentaries.

The Lancet HIV: Severe anti-LGBT legislations associated with lower testing and awareness of HIV in African countries
This first systematic review to investigate HIV testing, treatment and viral suppression in men who have sex with men in Africa finds that among the most recent studies (conducted after 2011) only half of men have been tested for HIV in the past 12 months.

The Lancet HIV: Tenfold increase in number of adolescents on HIV treatment in South Africa since 2010, but many still untreated
A new study of more than 700,000 one to 19-year olds being treated for HIV infection suggests a ten-fold increase in the number of adolescents aged 15 to 19 receiving HIV treatment in South Africa, according to results published in The Lancet HIV journal.

Starting HIV treatment in ERs may be key to ending HIV spread worldwide
In a follow-up study conducted in South Africa, Johns Hopkins Medicine researchers say they have evidence that hospital emergency departments (EDs) worldwide may be key strategic settings for curbing the spread of HIV infections in hard-to-reach populations if the EDs jump-start treatment and case management as well as diagnosis of the disease.

NIH HIV experts prioritize research to achieve sustained ART-free HIV remission
Achieving sustained remission of HIV without life-long antiretroviral therapy (ART) is a top HIV research priority, according to a new commentary in JAMA by experts at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

The Lancet HIV: PrEP implementation is associated with a rapid decline in new HIV infections
Study from Australia is the first to evaluate a population-level roll-out of pre-exposure prophylaxis (PrEP) in men who have sex with men.

Researchers date 'hibernating' HIV strains, advancing BC's leadership in HIV cure research
Researchers have developed a novel way for dating 'hibernating' HIV strains, in an advancement for HIV cure research.

Read More: HIV News and HIV Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.