Amino acids sequences-nucleotides compared

The functions of a large proportion of the proteins encoded by the human genome are presently unknown. Recent advances in bioinformatics permit researchers to compare amino acid sequences to discover clues to potential properties, physiologic roles, and mechanisms of action of proteins. Algorithms exploit the tendency of nature to employ variations of a structural theme to perform similar functions in several proteins (eg, the Rossmarm nucleotide binding fold to bind NAD(P)H,... 

Use the BLAST tool to compare the amino acid sequences for human a-lactalbumin and lysozyme. Repeat the process using BLAST to compare the nucleotide sequences for the genes coding for human a-lactalbumin and lysozyme. 

Figure 4 shows the deduced amino acid sequence from the nucleotide sequence of the two clones and compares it with the complete rice seed enzyme deduced amino acid sequence (9). There is a large amount of identity between the amino acid sequences, corresponding to about 76 . Most notable is the sequence between residues 424-434 in spinach leaf where it has been shown that Lys 431 is the site of chemical modification by PLP (7,9). There is complete agreement of this sequence in the same area with the rice seed enzyme sequence 462-472. Moreover, there is complete identity of the deduced amino acid sequences of amino acids 408-434 in the spinach leaf enzyme 51 kd subunit with amino acids 446-472 of the rice endosperm enzyme subunit. 

In addition to comparison of amino acid and nucleotide sequences of a-lactalbumin, and their rates of change as molecular clocks, a considerable amount of comparative information has accumulated on the three-dimensional structure of these proteins their physical properties in soludon effects of amino acid subsdtudons, in both genetic and cloned variants and their funcdons and immunological properties. In assessing this informadon it is important not to lose sight of the known paleontological informadon on the origin and evolution of mammals. 

Figure 1.1 Schematic depiction of the organization of ABC proteins. The minimal structural unit appears to consist of two integral transmembrane domains, each with (typically) six helical transmembrane spans, and two extrinsic nucleotide binding domains. At the amino acid sequence level, the nucleotide binding domains are relatively well conserved across the domains of life compared to the transmembrane domains.

---