Global Transition from D614 SARS-CoV-2 to G614 SARS-CoV-2 

- G614 was originally rare but became more prominent first in Europe, then in North America, Oceania, and Asia. 
- Sequences that exhibited part of of D614G 4-base haplotype (G614) were first found in China and Germany in late January, where the sequence only had three out of the four mutations found in D614G variant. In February 20, a sequence that exhibited all characteristics of a G614 was found in Italy. Many countries were found to have these variants soon after. 

University of Michigan - Ann Arbor

G614 is a variant of SARS-CoV-2 that is caused by a D614G amino acid change (A-G nucleotide change) in the S protein, which simultaneously also causes C-T mutations in three different areas of the spike

G614

https://doi.org/10.1016/j.cell.2020.06.043

Tracking changes in SARS-CoV-2 Spike: evidence that D614G increases infectivity of the COVID-19 virus

Origin and increased frequency of G614

An amino acid change to D614G, leading to the G614 variant, will eliminate the presence of the side chain hydrogen bond, causing an increase in mainchain flexibility and a change in protomer interactions. Glycosylatiom at a nearby N616 site can also be influenced by this change, which can affect the fusion peptide of the neighboring protomer 

Structural implications of the Spike D614G change


- The study obtained SARS-CoV-2 sequences from 999 individuals exhibiting COVID-19 symptoms from the Sheffield Teaching Hospitals NHS Foundation Trust. Information such as age, sex, date of sampling, hospitalization status, and cycle threshold (CT) were also included with the data. CT is used to determine a positive signal in E-gene based RT-PCR, where a lower CT indicate a higher viral load. The generalized linear model (GLM) showed that RT-PCR method and D614G status was statistically significant. Furthermore, G614 infections had lower CT values.
- D614G status and disease severity association were not statistically significant. Association between D614G status and hospitalizations were also not statistically significant.
- Regression analysis indicated that higher age, male sex, higher CT values were highly predictive of hospitalization. G614 status were not associated with higher hospitalizations.
- G614 status was found to be associated with higher fatality rate, although many factors may have contributed to this due to different countries with different responses to the disease

G614 is associated with potentially higher viral loads in COVID-19 patients but not with disease severity

- Pseudotyped single-cycle vesicular stomatitis virus (VSV) and lentiviral particles with D614 or G614 SARS-CoV-2 S protein were used to determine infectious titer. Viruses with G614 were found to have higher infectious titers than viruses with D614. 
- TMPRSS2 (type-II transmembrane serine protease) role is to cleave the viral spike protein after binding to receptor. Since the TMPRSS2 cleavage site is very close to the 614 spike, the study wanted to see if TMPRSS2 impacts the infectious titer of D614 and G614. 293T cells that expresses ACE2 receptor were infected in presence and absence of TMPRSS2, and viral titer was measured. They found that there was no difference in viral titer for D614 and G614, showing that TMPRSS2 does not impact viral titer, and infectivity is not enhanced
- The study also found that neutralization of G614-bearing pseudovirus was the same or better compared to that of D614-bearing pseudovirus. This shows that even though G614 have higher infectious titers, they are not more resistant to neutralization

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