Adaptive HIV-1 evolutionary trajectories are constrained by protein stability

Despite the use of combination antiretroviral drugs for the treatment of HIV-1 infection, the emergence of drug resistance remains a problem. Resistance may be conferred either by a single mutation or a concerted set of mutations. The involvement of multiple mutations can arise due to interactions between sites in the amino acid sequence as a consequence of the need to maintain protein structure. To better understand the nature of such epistatic interactions, we reconstructed the ancestral sequences of HIV-1’s Pol protein, and traced the evolutionary trajectories leading to mutations associated with drug resistance. Using contemporary and ancestral sequences we modelled the effects of mutations (i.e. amino acid replacements) on protein structure to understand the functional effects of residue changes. Although the majority of resistance-associated sequences tend to destabilise the protein structure, we find there is a general tendency for protein stability to decrease across HIV-1’s evolutionary history. That a similar pattern is observed in the non-drug resistance lineages indicates that non-resistant mutations, for example, associated with escape from the immune response, also impacts on protein stability. Maintenance of optimal protein structure therefore represents a major constraining factor to the evolution of HIV-1

Stability of Newcastle Disease Virus Strain V4-UPM Coated on Cassava Granules and Exposed to High Temperatures.

Protection of village chickens against Newcastle disease (ND) is considered feasible through food-delivered vaccines. Vaccine virus strain V4-UPM coated on cassava granules with or without additive (2% gelatin) was tested for stability at room temperature (RT) for 8 weeks and 40oC for 12 hours at weekly and two hourly intervals respectively. Stability was assessed by estimation of residual infectivity and infective virus excretion using standard methods. Results showed that at RT, the titre (EID50/gm) of the food vaccine with additive did not drop below the minimum effective immunogenic titre (MEIT) of 106.0 until after 4 weeks, whereas the one without additive dropped below MEIT value at the 3rd week of exposure. Following exposure at 40oC, the one with additive lost MEIT value after the 10th hour, while the infectivity of food vaccine without additive dropped below MEIT value after the 6th hour of exposure. Only four chickens produced HI antibody at first, whereas all 10 sero-converted on booster dose of vaccine, all 5 vaccinated and challenged birds resisted challenge, while all the unvaccinated control birds died. The vaccine virus was efficiently excreted by all birds that ate the food vaccine. It is hereby concluded that cassava granules sustained virus infectivity fairly enough for effective village chicken vaccination in any part of Nigeria