Bcl-2
Evolution and homologues
in other organisms
BLAST Searches and Analysis
BLAST stands for ‘Basic Local Alignment Search Tool’, and it is an algorithm for comparing primary biological sequence information, such as protein amino acid sequences or DNA nucleotide sequences. BLAST searches allow for comparison of a sequence with a database of other sequences, and it can identify statistically significant sequence matches.
C. elegans CED-9 Homologue
D. melanogaster Bcl-2 Homologue
H.sapiens Bcl-2 Alpha Isoform Homologue
M. musculus Bcl-2 Homologue
As seen when the BLAST images are lined up together for the H. sapiens, M. musculus, D. melanogaster and C. elegans homologues of Bcl-2, they all have relatively similar amino acid lengths. The H. sapiens and M. musculus proteins are close in length (239aa and 236aa respectively) but shorter than D. melanogaster and C. elegans (300aa and 280aa respectively) by at least 40 amino acids. All proteins have Bcl-2_like regions and all have BH3-homology region binding sites.
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In D. melanogaster and C. elegans, their BH4 domains reside inside the Bcl-2_like region along with the BH1, BH2 and BH3 domains. In H. sapiens and M. musculus, the BH4 domain is further away from the other BH domains, outside of the Bcl-2_like region. This could provide evidence for the mouse/human Bcl-2 homologues diverging down the same evolutionary path, as they both have this characteristic and fly/nematode do not. C. elegans, evolutionarily is the oldest homologue and has a non-specific BLAST hit for a zinc-peptidase-like domain which has apparently been lost during evolution. This would fit with the evolutionary cladogram.
Multiple Sequence Alignments and Analysis
A Multiple Sequence Alignment is a comparison of several DNA or amino acid sequences. It can be used to suggest and identify the presence of evolutionary relationships between the sequences, such as that from a shared lineage or common ancestor. The results can also suggest sequence homology, or a region that has been conserved among multiple sequences, which may indicate a particular importance or function for that domain.
MSA of H. sapiens vs M. musculus vs D. melanogaster vs C. elegans
When comparing the 4 sequences, it is seen that fruit fly and nematode have an additional section of protein that neither human nor mouse possess. It occurs between the location of the BH4 domain in mouse/human and the Bcl-2-like region found in all four organisms (see the BLASTs). The section was apparently lost during the evolutionary path that the mouse and human homologues took, perhaps it was found to be disadvantageous or unnecessary for the function of Bcl-2. Interestingly, the BH4 domain for fruit fly/nematode both start in this extended region (discovered by comparing BLASTs and the MSA) meaning that during evolution, mutations could have occurred that meant having the BH4 domain nearer the N-terminus was better for functionality.
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The area between all four species that had the most conservation/similarity of residues is in the Bcl-2-like region, generally in the BH3, BH2 and BH1 domain locations. When comparing this MSA and the 3 organism MSA (without C. elegans), it is seen that there are more similarities between the sequences in the Bcl-2-like region without C. elegans. This suggests that C. elegans is evolutionarily older as it is less similar to the other Bcl-2 homologues.
MSA of H. sapiens vs M. musculus vs D. melanogaster
When comparing these 3 sequences, it is seen that the human and mouse sequences align in almost exactly the same way to the drosophila sequence. This shows high similarity between these sequences, so a mouse vs human MSA was also done (see below).
MSA of H. sapiens vs M. musculus
There is very high similarity between these homologues. Almost all residues are matches between the two proteins, suggesting that these proteins could have diverged recently in evolutionary terms.
MSA of D. melanogaster vs C. elegans
There are conserved/similar regions outside of the Bcl-2-like region. There is large similarity between these two sequences, more so than if you compared either fruit fly or nematode to the human or mouse sequences. This suggests that fruit fly and nematode are more closely linked in evolutionary terms than the other two.
Cladogram
From the information deciphered from these MSAs, here is a cladogram representing the evolution of the Bcl-2 protein in the four organisms looked at.