PEGylation of protein side chains has been used for more than 30 years to enhance the pharmacokinetic properties of protein drugs. However, there are no structure- or sequence-based guidelines for selecting sites that provide optimal PEG-based pharmacokinetic enhancement with minimal losses to biological activity. We hypothesize that globally optimal PEGylation sites are characterized by the ability of the PEG oligomer to increase protein conformational stability; however, the current understanding of how PEG influences the conformational stability of proteins is incomplete. Here we use the WW domain of the human protein Pin 1 (WW) as a model system to probe the impact of PEG on protein conformational stability. Using a combination of experimental and theoretical approaches, we develop a structure-based method for predicting which sites within WW are most likely to experience PEG-based stabilization, and we show that this method correctly predicts the location of a stabilizing PEGylation site within the chicken Src SH3 domain. PEG-based stabilization in WW is associated with enhanced resistance to proteolysis, is entropic in origin, and likely involves disruption by PEG of the network of hydrogen-bound solvent molecules that surround the protein. Our results highlight the possibility of using modern site-specific PEGylation techniques to install PEG oligomers at predetermined locations where PEG will provide optimal increases in conformational and proteolytic stability.

There have been over 7 million cases and almost 413,372 deaths globally due to the novel coronavirus (2019‐nCoV) associated disease COVID‐19, as of June 11, 2020. Phylogenetic analysis suggests that there is a common source for these infections. The overall sequence similarities between the spike protein of 2019‐nCoV and that of SARS‐CoV are known to be around 76‐78% and 73‐76% for whole protein and receptor‐binding domain (RBD), respectively. Thus, they have the potential to serve as drug and/ or vaccine candidate. However, the individual response against 2019‐nCoV differs due to genetic variations in the human population. Understanding the variations in Angiotensin‐converting enzyme 2 (ACE2) and human leukocyte antigen (HLA) that may affect the severity of 2019‐nCoV infection could help in identifying individuals at higher risk from the COVID‐19. A number of potential drugs/vaccines as well as antibody/cytokine‐based therapeutics are running in various developmental stages of preclinical/clinical trials against SARS‐CoV, MERS‐CoV and 2019‐nCoV with substantial cross‐reactivity, which may be used against COVID‐19. For diagnosis, reverse transcription polymerase chain reaction (RT‐PCR) is the gold standard test for initial diagnosis of COVID‐19. Kit based on serological tests are also recommended for investigating the spread of COVID‐19 but it is challenging due to antibodies cross‐reactivity. This review comprehensively summarizes the recent reports available regarding the host‐pathogen interaction, morphological and genomic structure of the virus, and the diagnostic techniques as well as available and potential therapeutics against COVID‐19. This article is protected by copyright. All rights reserved.

Melittin is a good model antimicrobial peptide to understand the basis of its lytic activities against bacteria and mammalian cells. Novel analogues of melittin were designed by substituting the leucine residue(s) at the "d" and "a" positions of its previously identified leucine zipper motif. A scrambled peptide having the same composition of melittin with altered leucine zipper sequence was also designed. The analogues of melittin including the scrambled peptide showed a drastic reduction in cytotoxicity though they exhibited comparable bactericidal activities. Only melittin but not its analogues localized strongly onto hRBCs and formed pores of approximately 2.2-3.4 nm. However, melittin and its analogues localized similarly onto Escherichia coli and formed pores of varying sizes as tested onto Bacillus megaterium. The data showed that the substitution of hydrophobic leucine residue(s) by lesser hydrophobic alanine residue(s) in the leucine zipper sequence of melittin disturbed its pore-forming activity and mechanism only in hRBCs but not in the tested bacteria.

Protein PEGylation is an effective method for reducing the proteolytic susceptibility, aggregation propensity, and immunogenicity of protein drugs. These pharmacokinetic challenges are fundamentally related to protein conformational stability, and become much worse for proteins that populate the unfolded state under ambient conditions. If PEGylation consistently led to increased conformational stability, its beneficial pharmacokinetic effects could be extended and enhanced. However, the impact of PEGylation on protein conformational stability is currently unpredictable. Here we show that appending a short PEG oligomer to a single Asn side chain within a reverse turn in the WW domain of the human protein Pin 1 increases WW conformational stability in a manner that depends strongly on the length of the PEG oligomer: shorter oligomers increase folding rate, whereas longer oligomers increase folding rate and reduce unfolding rate. This strong length dependence is consistent with the possibility that the PEG oligomer stabilizes the transition and folded states of WW relative to the unfolded state by interacting favorably with side-chain or backbone groups on the WW surface.

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