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by Eric Martz
Black spots are mutations of concern in SARS-CoV-2 spike protein reported by UK scientists in December, 2020. RNA viruses mutate quickly so mutations are expected. These mutations may speed up contagion, but are unlikely to cause more severe COVID-19 and unlikely to reduce vaccine effectiveness. ACE2 binding residues. Animation shows priming via cleavage by furin.
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IB Tomasic, MC Metcalf, AI Guce, NE Clark, SC Garman. J. Biol. Chem. 2010 doi: 10.1074/jbc.M110.118588
The human lysosomal enzymes α-galactosidase and α-N-acetylgalactosaminidase share 46% amino acid sequence identity and have similar folds. Using a rational protein engineering approach, we interconverted the enzymatic specificity of α-GAL and α-NAGAL. The engineered α-GAL retains the antigenicity but has acquired the enzymatic specificity of α-NAGAL. Conversely, the engineered α-NAGAL retains the antigenicity but has acquired the enzymatic specificity of the α-GAL enzyme. Comparison of the crystal structures of the designed enzyme to the wild-type enzymes shows that active sites superimpose well, indicating success of the rational design. The designed enzymes might be useful as non-immunogenic alternatives in enzyme replacement therapy for treatment of lysosomal storage disorders such as Fabry disease.

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by Eric Martz
The Ramachandran Principle says that alpha helices, beta strands, and turns are the most likely conformations for a polypeptide chain to adopt, because most other conformations are impossible due to steric collisions between atoms. Check Show Clashes to see where non-bonded atoms are overlapping, and thus in physically impossible positions.

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