Human charged multivesicular body protein 1A (CHMP1A) displayed two bands on SDS–PAGE and differences in efficiency of complex formation with IST1. By site-directed mutagenesis and phosphate-affinity PAGE, we identified Ser179 and Ser182 located in the C-terminal region as major phosphorylation sites that cause a mobility shift, but interaction with IST1 was not affected by Ser-to-Ala mutations.
