Protein function evolution deletions

Structure analysis of several proteases involved in blood coagulation and fibrinolysis reveals a diverse, sometimes repetitive, assembly of discrete protein modules (Fig. 9.4) [56]. While these modules represent independent structural units with individual folding pathways, their concerted action contributes to function and specificity in the final protein product. On the genetic level, these individual modules are encoded in separate exons. Over the course of modular protein evolution, new genes are created by duplication, deletion, and rearrangement of these exons. Mechanistically, the exon shuffling actually takes place in the intervening intron sequences (intronic recombination - for further details see [10]). 

Indications of the structural features which are essential for a particular type of activity may be obtained by comparing the structure of different proteins which perform the same or similar functions. The characteristics which have remained unchanged during the course of evolution can thus be established. Such studies confirm that, as with the haemoglobins, there is considerable tolerance for replacement, deletion or insertion of amino acids in certain regions of the protein molecule. 

---