Component of the shieldin complex, which plays an important role in repair of DNA double-stranded breaks (DSBs). During G1 and S phase of the cell cycle, the complex functions downstream of TP53BP1 to promote non-homologous end joining (NHEJ) and suppress DNA end resection. Mediates various NHEJ-dependent processes including immunoglobulin class-switch recombination, and fusion of unprotected telomeres. Component of the shieldin complex, consisting of SHLD1, SHLD2, SHLD3 and MAD2L2/REV7. Within the complex, SHLD2 forms a scaffold which interacts with a SHLD3-MAD2L2 subcomplex via its N-terminus, and with SHLD1 via its C-terminus.