When a domain is not a domain.

The kinase regulatory-loop binding (KRLB) region of insulin receptor substrate 2 was originally thought to be a new type of domain with binding properties similar to phosphotyrosine binding (PTB) domains. A crystallographic study now shows that KRLB is actually a short peptide segment that binds to the insulin receptor using an extended series of contacts that mimic both autoinhibitory loop and ATP binding to its catalytic cleft.