Aha2 shares 45% sequence homology with Aha1, however, little is known about the functional protein. Aha1 is a member of the Hsp90 cochaperone family, and is thought to stimulate Hsp90 ATPase activity by competing with p23 and other co-chaperones for Hsp90 binding (1, 2).  It may affect a step in the endoplasmic reticulum to Golgi trafficking.  Aha1 also interacts with HSPCA/Hsp90 and with the cytoplasmic tail of the vesicular stomatistis virus glycoproteins (VSV G) (3).  Aha1 is expressed in numerous tissues, including the brain, heart, skeletal muscle, and kidney, and at low levels, the liver and placenta. Aha1 might be a potential therapeutic strategy to increase sensitivity to HSP inhibitors (4).