Ec. Dellangelica et al., BETA-3A-ADAPTIN, A SUBUNIT OF THE ADAPTER-LIKE COMPLEX AP-3, The Journal of biological chemistry, 272(24), 1997, pp. 15078-15084
Recent studies have described a widely expressed adaptor-like complex,
named AP-3, which is likely involved in protein sorting in exocytic/e
ndocytic pathways. The AP-3 complex is composed of four distinct subun
its. Here, we report the identification of one of the subunits of this
complex, which we call beta 3A-adaptin. The predicted amino acid sequ
ence of beta 3A-adaptin reveals that the protein is closely related to
the neuron-specific protein beta-NAP (61% overall identity) and more
distantly related to the beta 1- and beta 2-adaptin subunits of the cl
athrin-associated adaptor complexes AP-1 and AP-2, respectively. Seque
nce comparisons also suggest that: beta 3A-adaptin has a domain organi
zation similar to beta-NAP and to beta 1- and beta 2-adaptins, beta 3A
-adaptin is expressed in all tissues and cells examined. Go-purificati
on and co-precipitation analysesdemonstrate that beta 3A-adaptin corre
sponds to the similar to 140-kDa subunit of the ubiquitous AP-3 comple
x, the other subunits being delta-adaptin, p47A (now called mu 3A) and
sigma 3 (A or 8). beta 3A-adaptin is phosphorylated on serine residue
s in vivo while the other subunits of the complex are not detectably p
hosphorylated, beta 3A-adaptin is not present in significant amounts i
n clathrin-coated vesicles, The characteristics of beta 3A-adaptin rep
orted here lend support to the idea that AP-3 is a structural and func
tional homolog of the clathrin-associated adaptors AP-1 and AP-2.