ABSTRACT
As a first step of analysis, we can simply look at an alignment o f amino acid sequences of arthropodan lipocalins. A schematic representation of such an alignment is shown in Figure 1. The location of all important gaps is coincident with the loops (L) o f the β-barrel. While LI, L4 and L6 are relatively well conserved, all other loops accommodate significant variations in size. Particularly large extensions in L5 are present in one of the Pallidipin sequences, and in other lipocalins related to Nitrophorins (see below). Other expanded loops (L3 and L7) are also expected in these lipocalins. These three loops (L3, L5 and L7) face the entrance of the binding pocket (‘the open side of lipocalins\ see Chapter 3), and their variations could condi tion the ligand binding properties o f these lipocalins. Other lipocalins such as the Drosophila lipocalins GLaz and Karl show unique extensions in L2. Because this loop faces the closed side of the β-barrel, it is most probably involved in protein-protein interactions. Loop L3 o f GLaz is also long, but there is no sequence similarity with the L3 loop of R prolixus Pallidipin.
