We have seen the emergence of several variants of the COVID-19 virus. They have what seem to be strange names. As a beginning, let’s look at 3 of them:
THE ORIGINAL CHINA VARIANT called “G”: D614G
THE DENMARK MUTATION: L452R.
THE “Eeek”: MUTATION: E484K
What does the nomenclature of these variants mean?
It is actually quite simple.
Remember that proteins (like the Spike protein on the virus) are composed of a string of amino acids. There are 20 different amino acids and the order in which they are strung onto the string determines how that particular protein functions.
When looking at the Spike protein in COVID-19 variants, the number in the middle of the name marks the position in that string in which the mutation (the change) has occurred.
The letter at the position in front of the number is what the original amino acid was and the letter at the back of the number is the new changed amino acid. The single letters are an accepted international abbreviation for each of the 20 different amino acids.
So, for the Original China Variant, there was a change at position #614 from “D” to “G”, which translates as a change from Aspartic Acid to Glycine. Where the original protein had an aspartic acid residue at position 614, the variant now has a glycine residue there.
Now, if you remember from previous discussions, the mRNA molecules are instruction sheets to the cell that are used when manufacturing proteins. In the RNA, sequences of “bases” are used to tell the cell which amino acid to add to the protein string as it is being built. There are only a total of 4 bases in RNA, so individual bases cannot code for each amino acid singly. Instead, the RNA uses “codons” for instructions. Each codon is 3 bases long and can be any combination of the 4 bases.
The instruction to put an aspartic acid in position #614 is coded by “GAU”. Those are the three bases in a row, “G”= Guanine, “A”= Adenine and “U”= Uracil. GAU tells the cell to add an aspartic acid.
Now a “mutation” occurs when the RNA of the virus is reproduced with an error. In this case, the mRNA was reproduced with a “G” instead of the “A” in the codon. The codon for position #614 now reads “GGU”. There is an error there, a point mutation that now says to the cell, put a different amino acid at position #614. GGU codes for Glycine.
As you can see, a single “point mutation” in the mRNA in one of the bases in the codon for position #614 has resulted in the substitution of a Glycine amino acid for an Aspartic Acid amino acid. This is the new variant.
In the Denmark Variant the change is L452R.
This can now be read as a change in position #452 from Leucine to Arginine. And the codon change again was a single point mutation. What was originally “CUU”, has now been changed to “CGU” and that resulted in the amino acid change at position #452.
In the “Eeek” variation the change is E484K.
This can now be read as a change in position #452 from Glutamic Acid to Lysine. And the codon change again was a single point mutation. What was originally “GAA”, has now been changed to “AAA” and that resulted in the amino acid change at position #484.
The other variants with names like B.1.351 are named in a different way. This naming system uses a “hierarchical” system in which each variant group gets a letter name and then subgroups appear after the dot.