RGD Reference Report - The distinct nucleotide binding states of the transporter associated with antigen processing (TAP) are regulated by the nonhomologous C-terminal tails of TAP1 and TAP2.

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The distinct nucleotide binding states of the transporter associated with antigen processing (TAP) are regulated by the nonhomologous C-terminal tails of TAP1 and TAP2.
Authors:	Bouabe, H Knittler, MR
Citation:	Bouabe H and Knittler MR, Eur J Biochem 2003 Nov;270(22):4531-46.
RGD ID:	1300480
Pubmed:	PMID:14622282 (View Abstract at PubMed)
The transporter associated with antigen processing (TAP) delivers peptides into the lumen of the endoplasmic reticulum for binding onto major histocompatibility complex class I molecules. TAP comprises two polypeptides, TAP1 and TAP2, each with an N-terminal transmembrane domain and a C-terminal cytosolic nucleotide binding domain (NBD). The two NBDs have distinct intrinsic nucleotide binding properties. In the resting state of TAP, the NBD1 has a much higher binding activity for ATP than the NBD2, while the binding of ADP to the two NBDs is equivalent. To attribute the different nucleotide binding behaviour of NBD1 and NBD2 to specific sequences, we generated chimeric TAP1 and TAP2 polypeptides in which either the nonhomologous C-terminal tails downstream of the Walker B motif, or the core NBDs which are enclosed by the conserved Walker A and B motifs, were reciprocally exchanged. Our biochemical and functional studies on the different TAP chimeras show that the distinct nucleotide binding behaviour of TAP1 and TAP2 is controlled by the nonhomologous C-terminal tails of the two TAP chains. In addition, our data suggest that the C-terminal tail of TAP2 is required for a functional transporter by regulating ATP binding. Further experiments indicate that ATP binding to NBD2 is important because it prevents simultaneous uptake of ATP by TAP1. We propose that the C-terminal tails of TAP1 and TAP2 play a crucial regulatory role in the coordination of nucleotide binding and ATP hydrolysis by TAP.

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Biological Process

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Object Symbol	Species	Term	Qualifier	Evidence	With	Notes	Source	Original Reference(s)
Tap1	Rat	peptide antigen transport		TAS			RGD
Tap2	Rat	peptide antigen transport		TAS			RGD

Cellular Component

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Object Symbol	Species	Term	Qualifier	Evidence	With	Notes	Source	Original Reference(s)
Tap1	Rat	TAP complex		IDA			RGD

Molecular Function

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Object Symbol	Species	Term	Qualifier	Evidence	With	Notes	Source	Original Reference(s)
Tap1	Rat	ABC-type peptide antigen transporter activity		TAS			RGD
Tap2	Rat	ABC-type peptide antigen transporter activity		TAS			RGD
Tap2	Rat	ATP binding		IMP			RGD
Tap1	Rat	nucleotide binding		IDA			RGD
Tap2	Rat	nucleotide binding		IDA			RGD

Objects Annotated

Genes (Rattus norvegicus)

Tap1 (transporter 1, ATP binding cassette subfamily B member)

Tap2 (transporter 2, ATP binding cassette subfamily B member)

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The distinct nucleotide binding states of the transporter associated with antigen processing (TAP) are regulated by the nonhomologous C-terminal tails of TAP1 and TAP2.