Tag Archives: sheemei lok

Structure of the thermally stable Zika virus

by Victor A. Kostyuchenko, Elisa X. Y. Lim, Shuijun Zhang, Guntur Fibriansah, Thiam-Seng Ng, Justin S. G. Ooi, Jian Shi & Shee-Mei Lok

Nature (2016) doi:10.1038/nature17994  Published online 19 April 2016

Zika virus (ZIKV), formerly a neglected pathogen, has recently been associated with microcephaly in fetuses1, and with Guillian–Barré syndrome in adults2. Here we present the 3.7 Å resolution cryo-electron microscopy structure of ZIKV, and show that the overall architecture of the virus is similar to that of other flaviviruses. Sequence and structural comparisons of the ZIKV envelope (E) protein with other flaviviruses show that parts of the E protein closely resemble the neurovirulent West Nile and Japanese encephalitis viruses, while others are similar to dengue virus (DENV). However, the contribution of the E protein to flavivirus pathobiology is currently not understood. The virus particle was observed to be structurally stable even when incubated at 40 °C, in sharp contrast to the less thermally stable DENV3. This is also reflected in the infectivity of ZIKV compared to DENV serotypes 2 and 4 (DENV2 and DENV4) at different temperatures. The cryo-electron microscopy structure shows a virus with a more compact surface. This structural stability of the virus may help it to survive in the harsh conditions of semen4, saliva5 and urine6. Antibodies or drugs that destabilize the structure may help to reduce the disease outcome or limit the spread of the virus.

Read online: Nature.

CBIS PI Shee Mei Lok awarded National Research Foundation Investigatorship

Assistant Professor Lok is one of the recipients of the prestigious National Research Foundation Investigatorship.

Dengue Virus (DENV) infects approximately 100 million people each year. Increased travel, together with global climate change will result in further geographical expansion of the territory of the dengue mosquito vector, Aedes aegypti. There is an urgent need to develop safe and effective dengue therapeutics and vaccine.

CBIS-PI-portraits-sheemeiLok
CBIS PI Shee Mei Lok at the Titan Krios at the National University of Singapore Centre for BioImaging Research

In vitro experiments have shown that non-neutralizing antibodies can enhance DENV infection of Fc receptor bearing macrophages, one of the natural host cells for the virus. This suggested that the presence of non-neutralizing epitopes in a vaccine could potentially increase the chances that a person who had received the vaccine would develop the severe form of the disease, dengue hemorrhagic fever. For this reason, a more promising approach for engineering an effective DENV vaccine is to focus on including neutralizing epitopes. Thus, mapping of neutralizing epitopes is a necessary component of DENV vaccine research. Furthermore, understanding the neutralization mechanism of antibodies and the entry of DENV into the host cells also could aid in the design of targeted therapeutics.

The research in her laboratory therefore, focuses on the understanding of the pathology of dengue virus infection and the mechanism of neutralization by antibodies and other molecules so as to facilitate the development of suitable vaccines and therapeutics. A combination of molecular, immunological, biochemical and structural techniques (x ray crystallography and cryoEM image reconstruction techniques) will be used to achieve these aims.

Read more about Associate Professor Lok’s research.

Cryo-EM structure of an antibody that neutralizes dengue virus type 2 by locking E protein dimers

by Guntur Fibriansah, Kristie D Ibarra, Thiam-Seng Ng, Scott A Smith,  Joanne L Tan, Xin-Ni Lim, Justin S G Ooi, Victor A Kostyuchenko, Jiaqi Wang, Aravinda M de Silva, Eva Harris, James E Crowe Jr, Shee-Mei Lok

Science 3 July 2015: Vol. 349 no. 6243 pp. 88-91. DOI: 10.1126/science.aaa8651

There are four closely-related dengue virus (DENV) serotypes. Infection with one serotype generates antibodies that may cross-react and enhance infection with other serotypes in a secondary infection. We demonstrated that DENV serotype 2 (DENV2)–specific human monoclonal antibody (HMAb) 2D22 is therapeutic in a mouse model of antibody-enhanced severe dengue disease. We determined the cryo–electron microscopy (cryo-EM) structures of HMAb 2D22 complexed with two different DENV2 strains. HMAb 2D22 binds across viral envelope (E) proteins in the dimeric structure, which probably blocks the E protein reorganization required for virus fusion. HMAb 2D22 “locks” two-thirds of or all dimers on the virus surface, depending on the strain, but neutralizes these DENV2 strains with equal potency. The epitope defined by HMAb 2D22 is a potential target for vaccines and therapeutics.

Read the entire article.

Learn more about Shee-Mei Lok’s research.