13qC3. View the map and BAC contig (data from UCSC genome browser).
Ap3b1/NM_009680: 27 exons, 207,285bp, chr13:92,605,147-92,812,431.
Note: Alternate name is adaptor-related protein complex 3 beta 1 (Ap3b1 or A3b1).
The figure below shows the structure of the Ap3b1 gene (data from UCSC genome browser).
Search the 5'UTR and 1kb upstream regions (human and mouse) by CONREAL with 80% Position Weight Matrices (PWMs) threshold (view results here).
Tissue specificity: ubiquitously expressed. Ap3b1 produces a mRNA transcript of ~4.2-kb, detectable by Northern blots in kidney, heart, bone marrow, eye, and macrophages.
Affymetrix microarray expression pattern in SymAtlas from GNF is shown below.
Beta3A-adaptin (NP_033810): 1105aa, ExPaSy NiceProt view of Swiss-Prot:Q9Z1T1.
Synonyms: Adapter-related protein complex 3 beta 1 subunit; Adaptor protein complex AP-3 beta-1 subunit; AP-3 complex beta-1 subunit; Clathrin assembly protein complex 3 beta-1 large chain.
|Protein||NP_033810 (1105aa)||AAP45786 (1091aa)||XM_226666 (1171aa)||AAF71924 (1160aa)||Apl6p (809aa)|
|Identities||86% /965aa||85% /951aa||86% /1028aa||49% /575||26% /209|
View multiple sequence alignment (PDF file) by ClustalW and GeneDoc.
(1) Domains predicted by SMART:
a) low complexity: 10 - 24
b) low complexity: 275 - 291
c) coiled coil: 677 - 700
d) low complexity: 761 - 802
(2) Transmembrane domains predicted by SOSUI: none.
(3) Pfam domains: PF01602 - Adaptin N terminal region.
(4) CDD conserved domain: KOG1060, vesicle coat complex AP-3, beta subunit (Intracellular trafficking, secretion, and vesicular transport).
(5) Graphic view of InterPro domain structure.
(1) Predicted results by ScanProsite:
a) N-glycosylation site [pattern] [Warning: pattern with a high probability of occurrence]:
75 - 78 NASE, 402 - 405 NIST, 861 - 864 NLST, 870 - 873 NVST, 919 - 922 NTSD, 983 - 986 NVTL, 1015 - 1018 NETS.
b) Tyrosine sulfation site [rule] [Warning: rule with a high probability of occurrence]:
267 - 281 edneknfYeseeeee.
c) cAMP- and cGMP-dependent protein kinase phosphorylation site [pattern] [Warning: pattern with a high probability of occurrence]:
288 - 291 RKkS, 752 - 755 KRnS, 758 - 761 KRkS.
d) Tyrosine kinase phosphorylation site [pattern] [Warning: pattern with a high probability of occurrence]:
345 - 352 RsnrEvq.Y
e) Neutral zinc metallopeptidases, zinc-binding region signature [pattern]:
879 - 888 TktHELLHrM.
(2) Predicted results of subprograms by PSORT II:
a) N-terminal signal peptide: none
b) KDEL ER retention motif in the C-terminus: none
c) ER Membrane Retention Signals: none
d) VAC possible vacuolar targeting motif: found KLPI at 923
e) Actinin-type actin-binding motif: type 1: none; type 2: none
f) Prenylation motif: none
g) memYQRL transport motif from cell surface to Golgi: none
h) Tyrosines in the tail: too long tail
i) Dileucine motif in the tail: found LL at 114
ModBase: predicted comparative 3D structures on Q9Z1T1 (data from UCSC Gene Sorter). (from left to right: Front, Top, Side view)
This protein does not exist in the current release of SWISS-2DPAGE.
Computed theoretical MW=122,870Da, pI=5.49 (NP_033810).
a) Biological process: intracellular protein transport (overview of trafficking pathway here).
b) Biological process: endocytsis c) Component of Golgi apparatus.
d) Plays a role in protein sorting in the late-Golgi/trans-Golgi network (TGN) and/or endosomes.
e) Plays a role in the vesicular trafficking of tyrosinase to melanosomes (view diagram of melanosomal protein sorting here).
Component of the coat surrounding the cytoplasmic face of coated vesicles located at the Golgi complex.
The Ap3b1 gene encodes the adapter-related protein complex 3 beta 1 subunit (beta-adaptin 3A, or AP-3 complex beta-3A subunit). The AP-3 complex is a heterotetramer composed of two large adaptins (delta/AP3D1 and beta3A/AP3B2 or beta3B/AP3B1), a medium adaptin (mu3A/AP3M1 or mu3B/AP3M2) and a small adaptin (sigma3A/AP3S1 or sigma3B/AP3S2). In addition, the AP3M1 subunit interacts with tyrosinase for lysosomal targeting (Honing, et al). In pearl cells, the delta and sigma3 subunits coassemble into a heterodimer, whereas mu3 gets destroyed. The hinge and/or ear domains of beta3 are important for function, but the clathrin binding site is not needed (Peden, et al). AP-3 complex interacts with CD1 antigen presenting molecules. Benson, et al reported that C-terminal processing of neutrophil elastase exposes an AP3 interaction signal responsible for redirecting neutrophil elastase trafficking from membranes to granules. More cargoes for AP-3 complex are reviewed by Dell'Angelica (2009).
6 proteins are shown to be associated with APL6 in Yeast GRID.
Ap3b1 drosophila homolog CG11427 interaction information in CuraGen interaction database.
AP-3 complex is associated with the Golgi region as well as more peripheral structures. It facilitates the budding of vesicles from the Golgi membrane and appears to be involved in the sorting of a subset of transmembrane proteins targeted to lysosomes and lysosome-related organelles. In yeast, AP-3 sorts the vacuolar membrane enzymes,alkaline phosphatase and Vamp3p, a vacuolar t-SNARE (Odorizzi, et al). Faundez, et al found that the AP-3 complex is involved in synaptic vesicle formation in neuronal cells. Likewise, Sugita, et al proposed that there is an AP-3 dependent pathway for antigen presentation by CD1B (human) or CD1d (mice) molecules. More details in the description of the AP-3 dependent pathways are descriped in the human HPS2.
AP-3 interacts with HOPS complex or BLOC-1 in protein trafficking to lysosomes or LROs. However, the mechanism of AP-3 dependent pathway is distinct from that dependent on HPS1 (BLOC-3) (Feng, et al (2002))(view diagram of BLOC-3 and AP-3 pathway here). Hps2 may play a role in the late stages of the maturation of melanosomes (Nguyen, et al) (view diagram of melanosome blockage and melanosomal protein sorting here).
SNPs deposited in dbSNP.
|Exon 8||del exons 8~15||787G~1653G del 867bp (exons 8~15 )||D263~Q551 del 289aa||in-frame||pe-9J (B6)||Feng, et al (2000)|
|Exon 19||dup exons 19~24, ins 215bp partial transposon||2135A~2927G dup 793bp (exons 19~24)||E712dup 793bp||frame-shift, 976X||pe (B6)||Feng, et al (1999)|
|Exon 22||del exon 22||2504T~2610C del 107bp (exon 22)||W835del 107bp||frame-shift, 847X||pe-8J (DBA/2J)||Feng, et al (1999)|
All the three allelic mutations involve in large deletion or insertion in the genome. The encoded Ap3b1 subunit or other subunits of AP3 complex are missing or destablized by Western blot analysis (Feng, et al (1999; 2000); Zhen, et al ).
Defects in AP3B1 are the cause of the autosomal recessive phenotype 'pearl' (pe), a mouse model of Hermansky-Pudlak syndrome type 2 (HPS-2, OMIM 608233 ). The pe allele arose spontaneously from C3H/He, was transferred to C57BL/6J. The strain is described in more detail in JAX Mice database (B6.C3-Ap3b1pe/J). Homozygous mutants exhibit hypopigmentation, elevated kidney levels of lysosomal enzymes, platelet storage pool deficiency, reduced ipsilateral projections from the retina to brain (Novak, et al), reduced sensitivity of dark-adapted retina (night blindness) and shortened life span. In the Ap3b1/pe mutants, very small numbers of melanosomes are observed in the RPE, and melanosomes of the choroid are fewer in number and exhibit greater size heterogeneity than controls (Feng, et al (2002)). See more in details in Mouse Locus Card#Ap3b1. The transposonal mutation in pe may lead to the reversion of the mutation in peR (Feng, et al (2000)).
The CTL lytic granules present decreased secretion of in pearl mutant. CTL killing is severely impaired because of the loss of secretory lysosome polarization. The secretory lysosomes remain in the periphery of the cell, apparently stuck at the ends of microtubules (Clark, et al) (view diagram of lytic granule blockage in CTL cells here). AP-3 is most likely crucial for sorting a protein required for lysosomal polarization in CTL. Missorting of CD1d occurs in cells of the pearl and mocha (view diagram of CD1d blockage in APC cells here). In contrast, a wide variety of studies have noted normal peptide antigen presentation by the MHCII pathway in AP-3 deficient cells of mice and humans. Significantly lower NKT cell levels are found in spleen, thymus and liver of AP-3 deficient mice (Cernadas, et al). Benson, et al have found that frameshift mutations in the Ap3b1 subunit of AP-3 in the gray collie lead to unexpected consequences for levels of circulating leukocytes. The resulting loss of AP-3 function leads to hypopigmentation and the stem cell disease, cyclic hematopoiesis.
By homologous recombination, Yang, et al found that the Ap3b1 gene was disrupted in the null phenotype, Ap3b1(LN), which displayed phenotypes similar to those of pearl mice. Moreover, pearl is likely to be a hypomorph as the Ap3b1(LN) homozygotes had a lighter coat color and accumulated fewer of the mu3 and delta3 subunits of AP-3 than did pearl mice. Immunofluorescence analysis of fibroblasts and melanocytes cultured from Ap3b1(LN) homozygotes revealed that the lysosomal membrane proteins Lamp I and Lamp II and the melanosomal membrane protein tyrosinase were mislocalized. In particular, the Lamp proteins were clustered on the cell surface. These findings are similar to the observations in HPS-2 fibrablasts with the mislocalization of lysosomal proteins such as CD63, LAMP-1, LAMP-2, and LAMP-3 (Dell'Angelica, et al).
Lyerla et al demonstrated a mouse model of HPS, which is homozygously recessive for both the Hps1 (pale ear) and Hps2 (pearl) genes (Feng, et al (2002)), exhibits striking abnormalities of lung type II cells. Type II cells and lamellar bodies of this mutant are greatly enlarged, and the lamellar bodies are engorged with surfactant. Giant lamellar bodies (GLB) formation is not associated with abnormal trafficking or recycling of surfactant material. Instead, impaired secretion is an important component of GLB formation in ep/pe mice (Guttentag, et al). HPS double mutant ep/pe mouse strain develops interstitial pneumonia (HPSIP) past 1 year of age, which may be initiated by abnormal ATII cells and exacerbated by alveolar macrophage activation with elevated level of TGFbeta1 (Wang and Lyerla). Inflammation is initiated from the abnormal alveolar epithelial cells in ep/pe double mutant, and S-nitrosylated SP-D plays a significant role in amplifying pulmonary inflammation (Atochina-Vasserman, et al). Aberrant surfactant trafficking and secretion may lead to the apoptosis of alveolar epithelial type II cell in HPSIP, thereby causing the development of HPSIP (Mahavadi,et al). To study the pulmonary inflammation, cultured pearl alveolar macrophages (AMs) had markedly increased production of inflammatory cytokines at baseline, although baseline bronchoalveolar lavage (BAL) cell counts and differentials were similar in pearl and strain-matched wild-type mice. The lungs of ep and pe mice exhibit hyperresponsiveness to LPS and constitutive and organ-specific macrophage activation (Young, et al).