The asymmetric unit consists of one light and one heavy chain. This has been done by PPS Consultant Will Pitt- click for the resulting structure file . You can obtain the coordinate file of a model of an entire human IgG1 molecule , on Eric Martz' RasMol Home Page , at the University of Massechusetts Amherst. The file was provided by Eduardo Padlan of the National Institutes of Health, Bethesda. Papain and pepsin both cleave the heavy chains between the 2nd and 3rd domains.
Papain cleaves on the N-terminal side of the two disulphide bonds linking the two heavy chains.
Click here for the crystal structure of an Fab fragment. Protein Modules, Trends in Biochem.