Assembles to form an icosahedric capsid shell with a T=7 symmetry although with a diameter of about 82 nm, which is a larger volume than the usual T=7 capsids (PubMed:30737287). A dramatic reconfiguration of the capsid shell that expands the procaspid from a diameter of 66 nm to a supersized capsid of 82 nm, allows packaging of the large viral DNA genome (PubMed:30737287). The capsid decoration protein binds the expanded capsid and stabilizes it (PubMed:30737287). Homomultimer (PubMed:30737287). Interacts with the portal protein (Probable). Interacts with the decoration protein (PubMed:30737287). Forms the capsid icosahedric shell. Belongs to the lambda phage major capsid protein family.