From this figure, it appears that human lysozyme and mouse lysozyme are most closely related. On a more puzzling note, none of the first 35 aa's in the human lysozyme are conserved. Although it is difficult to determine the most primitive sequence, the human lysozyme sequence seems to have mutated significantly from it. Whether there is a function significance or an evolutionary significance to the human protein, is equally difficult to tell, but a sequence comparison on a much larger scale might provide more insight. Proposed Phylogenetic Tree From the sequence alignment produced in Fig. 5, a phylogenetic relationship for lysozyme was constructed.
Numbers indicate lysozyme percentage aa sequence conservation between shown organisms.
This proposed tree confirms the close relation of the human, mouse, and to a lesser degree, fly, E. coli , and chicken lysozyme proteins. It is clear that this tree is not wholly consistent with evolutionary lineage. One would expect that the mouse would be most conserved, followed by the chicken, the fly, and E. coli . A plausible explanation for this is the selection pressures exerted on domesticated chickens. Since domesticated chicken have a high exposure rate to bacterial infection, it is consistant that a defense mechanism, such as lysozyme, might be highly mutated.