The scaffold protein NBR1 is involved in signal transmission downstream of the serine/protein kinase from the giant muscle protein titin. Its N‐terminal Phox and Bem1p (PB1) domain plays a critical role in mediating protein–protein interactions with both titin kinase and with another scaffold protein, p62. We have determined the crystal structure of the PB1 domain of NBR1 at 1.55 Å resolution. It reveals a type‐A PB1 domain with two negatively charged residue clusters. We provide a structural perspective on the involvement of NBR1 in the titin kinase signalling pathway.