NIAID-DVI: Understanding the E gene Part II: 3 Tales of the power of small changes

Now that we have an appreciation for the dynamic dengue particle back to the ever elusive E gene...

Small Change #1: 2 amino acids

The type-specific neutralizing antibody response elicited by a dengue vaccine candidate is focused on two amino acids of the envelope protein
Ted Pierson
NIAID-NIH

As stated in many of these blog series posts the failure of the Sanofi vaccine has highlighted the limited understanding we still have about dengue and the research continues in many aspects of disease pathogenesis as well as genetic influences on the virus. Ted Pierson (and others) seek to better understand the humoral immune response against DENV infection. They wanted to identify epitopes recognized by serotype-specific neutralizing antibodies elicited by monovalent DENV1 vaccination. To do this they constructed a panel of over 50 DENV1 structural gene variants containing substitutions at surface accessible residues of the envelope protein to match the corresponding DENV2 sequence. They identified two mutations that contribute significantly to type-specific recognition by polyclonal DENV1 immune sera. When they analyzed sera from 24 participants of a phase I clinical study, they found that there was a reduced capacity to neutralize a DENV1 variant which contained both mutations. Sera from 77% of subjects recognized the DENV1 variant and DENV2 equivalently (less than 3 fold difference). The data indicated that the type-specific component of the DENV1 neutralizing antibody response to vaccination was focused on just two regions of the E protein. The amino acids in question? E157 and E126.

Unfortunately the paper hasn't come out specifically on this study that I can find...but Pierson has been involved in numerous studies characterizing aspects of the E gene:

• Shrestha et al., 2012. Complex phenotypes in mosquitoes and mice associated with neutralization escape of a dengue virus type 1 monoclonal antibody. Virology 427: 127
• Austin SK, et al., 2012 Structural Basis of Differential Neutralization of DENV-1 Genotypes by an Antibody that Recognizes a Cryptic Epitope. PLoS Pathog 8(10): e1002930
• Sukupolvi-Petty et al., 2013. Functional analysis of antibodies against dengue virus type 4 reveals strain-dependent epitope exposure that impacts neutralization and protection. JVI ahead of print.
• Pierson and Kielian. 2013. Flaviviruses: braking and entering. Curr Opin Virol 3:3

Small Change #2: The fusion loop of the E gene

NIAID-DVI: The Dynamic Dengue Particle -- Richard Kuhn

New Lessons in dengue virus structure and composition and their influence on vaccine strategies
Richard Kuhn
Purdue University

I had the honor and pleasure of meeting Dr. Kuhn where I work and he is fantastically animated and I very much enjoyed listening to what he had to say.

The structure of dengue has been known for more than 10 years via cryo-electron microscopy; however now with more sophisticated tools we can see the virus in ways unimaginable in the past. His group employed a variety of structure and biochemical tools to probe the structure of the dengue virion as well as conformation, composition and dynamics..

Lets look at some particles...

mmm...pretty. Clustering of dengue particles. Source: MicrobiologyBytes