Final answer:
Different versions of the BLOSUM matrix exist to account for the variation in evolutionary distances between proteins, with each version constructed from alignments with specific sequence identity thresholds, such as BLOSUM62 for more divergent proteins and BLOSUM80 for closely related proteins.
Step-by-step explanation:
The different versions of the BLOSUM matrix exist because proteins evolve at different rates, and matrices are constructed based on different levels of sequence similarity to reflect this variety in evolutionary distance. The BLOSUM matrices are used for scoring alignments between protein sequences. To tailor the alignment score for varying degrees of sequence conservation, different BLOSUM matrices are created from alignments of sequences that share a certain percentage identity. For instance, BLOSUM62 is derived from sequences with no more than 62% identity, while BLOSUM80 is based on sequences with no more than 80% identity. Matrices like BLOSUM62 cater to more divergent proteins while BLOSUM80 is suitable when aligning more closely related proteins.