Cloning and characterization of a 22 kDa protein from rat adipocytes: a new member of the reticulon family

In the course of our examination of proteins associated with the GLUT4-cont aining vesicles of rat adipocytes we have identified a new 22 kDa member of the family of endoplasmic reticulum (ER) proteins known as reticulons. The protein, which we refer to as vp20, was purified from a preparation of GLU T4-containing vesicles of rat adipocytes, and tryptic peptides were micro-s equenced. From this information a cDNA encoding a single open reading frame for a protein of 22 kDa was cloned. This protein is homologous to known me mbers of the reticulon protein family. vp20 has two hydrophobic stretches o f about 35 amino acids that could be membrane spanning domains and an ER re tention motif at its carboxy-terminus. vp20 was most abundant in the high d ensity microsome fraction of adipocytes, which is the fraction most enriche d in ER. Only a small fraction of vp20 was present in the GLUT4 vesicle pop ulation, and that fraction appears to be due to ER vesicles that were non-s pecifically bound to the adsorbent. Analysis of tissue distribution of vp20 in rats revealed that it is concentrated in muscle, fat and the brain. (C) 1999 Elsevier Science B.V. All rights reserved.