The immunoglobulin homology unit

The qualifying feature of the immunoglobulin homology unit is its molecular architecture. Delineation of this structure has resulted from a considerable amount 

Two types of immunoglobulin units can be distinguished V and C ([7], Fig. 1 and Table 1). Seven /8-strands (A to G) are found in both types. However, V units contain two additional /8-strands (C and C ) as part of an extra hairpin loop between the C and D strands. VL and VH units are also distinguishable on the basis of a few critical residues [8,9]. 

Folding pattern characteristic of immunoglobulin units is suggested by  

-strand motifs these show a prevalence of replacements, rather than of insertions/deletions 

V units have an extra hairpin loop and two extra /3-strands (C and C ). The latter are found in a five-stranded /3-sheet with strands C, F and G. As a consequence, the number of residues between the disulphide-bonded cysteines is higher in V ( 70) than in C (—60) units  

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