Neuregulin 1 (NRG-1) is a member of the neuregulin family (along with NRG 2-4). Each member of this family is encoded by an individual gene. Alternative splicing and different promoter utilisation results in a large number of isoforms for each member of the protein family – for example, NRG-1, the best studied member, generates six types of protein (I–VI) and at least 31 isoforms (https://www.nature.com/articles/nrn2392). These isoforms have different tissue distribution, potency, receptor specificity and biological functions (https://link.springer.com/content/pdf/10.1007/s00018-007-7120-0.pdf).
All NRG-1 isoforms contain the bioactive EGF-like domain, this EGF-like domain has two isoforms: alpha and beta. These differ in their receptor affinity; both the alpha and beta isoforms are ligands for the receptors ErbB3 (HER3) and ErbB4 (HER4), however the NRG-1 beta isoform has a higher affinity for the ErbB4 receptor than the alpha isoform (https://www.nature.com/articles/1205960). This protein (Qk045) consists of the β isoform of the EGF domain of NRG-1 protein.
NRG-1 has an essential role in cardiac and neuronal development, and is implicated in disorders such as schizophrenia (https://www.nature.com/articles/s41398-020-00868-5), and numerous cancers, for example breast cancer where NRG-1 promotes the proliferation and migration of breast cancer cells (https://www.nature.com/articles/s41388-021-01719-3). In cell culture, NRG-1 is frequently used in maintenance media for human pluripotent stem cells and other cells.