Calmodulin: Linking Conservation and Evolution Through Orthologs

Further Investigations Using ClustalW2

(Note: Using BLAST to search for orthologs of the human calmodulin I gene or protein sequence gives too many hits for the same species and therefore was not a very helpful tool for this widespread protein. Therefore other calmodulin seuqences were discovered using NCBI and aligned to search for sequence conservation using ClustalW2).

Alignment of Eukaryotic Sequences

In order to obtain visual information about the conservation of the calmodulin protein sequence among eukaryotes I used ClustalW2 to align a myriad of distinct eukaryotic calmodulin protein sequences. The table below indicates which eukaryotic species are aligned and the link from each accession indicates the source of the sequence information (obtained from NCBI).

Below is the ClustalW2 results from the calmodulin protein sequence alignment of the above various eukaryotes. The default settings for ClustalW2 alignment were used.

As you can see from the above alignment, the protein sequence for calmodulin is highly conserved between various and extremely different eukaryotic species from corn to zebrafish to protazoans. My alignments using ClustalW2 support the literature findings that calmodulin is found in various eukaryotes (and in fact an NCBI protein search for calmodulin leads to 1031 pages of verified calmodulin protein hits from different species) and that the sequence for calmodulin is highly conserved among these different species. This strong conservation indicates an evolutionary importance behind the primary structure. In other words the fact that the calmodulin protein sequence is conserved in various eukaryotes indicates that the protein sequence is important for the proper functioning of the protein. In fact in the case of calmodulin (being a shorter protein of only 149 amino acids) it appears that most of the amino acid residues (most likely making up the 4 calcium binding sites) need to be conserved for proper functioning.

Alignment of Big Seven Sequences

The big seven genomic species are a benchmark for many researchers. The below table indicates the 7 species and information about the existence of calmodulin within such species. For the species with confirmed existence of calmodulin, the species specific calmodulin sequences are compared using ClustalW2.

Below is the alignment of the 6 sequences of the eukaryotes with document calmodulin. The default settings from ClustalW2 were used again.

In the above alignment you see more variation than in the previous alignment, this is mainly because of the yeast calmodulin sequence. Despite the decrease in identical calmodulin protein sequences, we must still look at the conservation of amino acids with the same properties, which is partially indicated by the color scheme. The alignment symbol : indicates an alignment of amino acids at that position that maintain the same properties according to the ClustalW2 groupings of properties. The importance of conservation is in the conserved structure of calmodulin (recall structure dictates function), which is supported by the conservation of the primary amino acid sequence not only in exact identical sequences but also in conserved amino acids with similar properties. The above alignment still indicates a highly conserved primary amino acid sequence and potentially a highly conserved tertiary structure of calmodulin when taking into account conservation of amino acids with similar properties.

My Home Page

Molecular Biology Homepage

Davidson College Homepage

Please direct questions or comments to karicheson@davidson.edu