Regulatory subunit of anion-selective CLCNKA:BSND and CLCNKB:BSND heteromeric channels involved in basolateral chloride conductance along the nephron to achieve urine concentration and maintain systemic acid-base homeostasis, and in the stria vascularis of the inner ear to establish the endocochlear potential necessary for normal hearing. Most likely acts as a chaperone that allosterically regulates proper sorting of CLCNKA:BSND and CLCNKB:BSND channels at the basolateral plasma membrane domain and functional switch to ion conducting state. Mediates constitutive opening of channel common gates