The Eukaryote Linear Motif resource for Functional Sites in Proteins
Accession:
Functional site class:
di Arginine retention/retrieving signal
Functional site description:
The di-Arg ER retrieval and retention motif is present on membrane proteins where it serves for ER localisation. A variety of membrane proteins (some multimeric) possess this di-Arg motif. Here the motif functions as a quality control mechanism for correct folding and protein complex assembly governing the ER exit. The functional motif needs to be exposed within a cytosolic region of the membrane protein and requires a distinct proximity to the transmembrane region. Heteromerization, as well as the interaction with 14-3-3 proteins or PDZ domain containing proteins can render some di-Arg retention signals inactive, whereas the interaction with Coat protein complex I (COPI) supports ER retrieval. Finally, some di-Arg based ER-retention signals may be negatively regulated by phosphorylation of nearby residues.
ELM Description:
The di-Arg motif is present on the cytosolic side of many transmembrane proteins and serves as an ER-retrieval and retention motif. It is defined by two arginine residues, either next to each other or spaced by a single unconserved (RR, RXR). Longer insertions have been reported such as RXXR but we chose not to extend the motif in ELM due to the limited literature (Boulaflous,2009, Uemura,2009). Either before or after the Arg pair, there is a hydrophobic residue or a third Arg (Michelsen,2005). This implies that the motif may have two binding orientations, though this is not yet known. A combinatorial screening approach for the RXR sequence revealed that negatively charged or small, non-polar residues surrounding the arginines negatively affect the motif activity, whereas three or more arginines provide a strong ER-retention efficiency (Zerangue,2001). It is likely that the motif must be linked to one or more transmembrane regions and the distance from the transmembrane region to the di-Arg motif may be important (Zhang,2008, Michelsen,2005). Any di-Arg motif matches in non-membrane proteins should be disregarded.
Pattern: ([LIVMFYWPR]R[^YFWDE]{0,1}R)|(R[^YFWDE]{0,1}R[LIVMFYWPR])
Pattern Probability: 0.0053693
Present in taxon: Eukaryota
Interaction Domain:
WD40 (PF00400) WD domain, G-beta repeat (Stochiometry: 1 : 1)
o See 27 Instances for TRG_ER_diArg_1
o Abstract
The trafficking of proteins between vesicular compartments and delivery of proteins to particular subcellular locations are tightly regulated and essential for instance to achieve correct assembly of multimeric proteins and correct post-translational modifications. Arginine-based sorting motifs are shown to be critical in the biosynthetic processing of numerous transmembrane proteins. Schutze,1994 first described a di-Arg ER-retention motif determined by two adjacent Arginines (RR) localized on one form of the invariant chain (Ii33, P04233) of the major histocompatibility complex (MHC) class II (Schutze,1994). The initial presumptions of a required proximity to the N terminus and specificity for type II membrane proteins have been superceded. The di-Arg motif is most commonly found on an N- or C-terminal cytosolic region but can be found at other cytosolic protrusions of polytopic membrane proteins (Michelsen,2005). In the context of studying assembly and trafficking of ATP sensitive K+ channels (K-ATP), Zerangue,1999 found another variant of the di-Arg motif within the K-ATP subunits Kir6.1 (Q15842), Kir6.2 (Q14654) and SUR1 (Q09428). Mutational analysis and chimeric fusion proteins revealed an RXR-based sequence retaining single K-ATP subunits and incorrectly assembled complexes in the ER, preventing surface expression.
The di-Arg motif is not only present in K-ATP channel subunits but also in subunits of additional heteromeric membrane proteins like GABA (Q9UBS5), Kainate (Q16478) and NMDA (Q05586) receptors. Here the di-Arg ER-localization motif functions as a quality control mechanism governing the ER exit. Single subunits of unassembled multimeric proteins with an exposed di-Arg motif, which is suggested to be recognized by generic eukaryotic trafficking machinery, are retained in the ER. Only properly folded and fully assembled protein complexes can leave the ER and reach the cell surface (Zerangue,1999, Taneja,2009). Therefore the di-Arg motif represents a checkpoint for both the coordination of sequential assembly of multimeric membrane proteins and the regulation of their delivery to the cell membrane defining the number of protein complexes at the cell surface (Scott,2001). Precise regulation mechanisms are still unknown, but a simple explanation for the regulation of di-Arg based ER-retention in terms of surface expression of multimeric proteins is an inhibition of the motif by steric masking during heteromerization. Furthermore, the interaction with additional proteins like coat protein complex I (COPI), 14-3-3 proteins as well as PDZ domain containing proteins may act as regulatory switches. For example, unassembled K-ATP subunits possessing an exposed RXR motif are shown to be recognized by the COPI machinery and retrieved to ER by COPI coated vesicles, defining the di-Arg motif as an ER retrieval and retention motif (Taneja,2009). By contrast, 14-3-3 proteins may be qualified to probe the assembly status of multimeric membrane proteins and are often required in order to negatively regulate the di-Arg motif. 14-3-3 proteins reduce COPI mediated retention, which is necessary for the forward transport of the assembled protein complexes (Yuan,2003, Taneja,2009, Heusser,2006). For some instances (ADAM22 (Q9P0K1) and GPR15 (P49685) the 14-3-3 binding sequence overlaps with the di-Arg ER-retention motif, again indicating a regulatory switch by steric masking controlled by basophilic kinases, since 14-3-3 proteins bind phosphopeptides. Additionally, the di-Arg motif present in an NR1 (Q05586) subunit can be masked by recruitment of PDZ domain containing proteins (Scott,2001). Finally, di-Arg based ER-retention is likely regulated by phosphorylation of nearby residues. Either phosphomimetic mutations or activation of PKC enhanced the surface delivery of NR1, suggesting an inhibitory effect on di-Arg based ER-retention (Scott,2001). The CFTR protein is an unusual case. Cryptic di-Arg motifs are thought to become active due to cystic fibrosis unfolding mutations such as at F508 (Chang,1999). The instance in ELM is annotated as a false positive as this di-Arg is not a normal cellular motif.
o 12 selected references:

o 12 GO-Terms:

o 27 Instances for TRG_ER_diArg_1
(click table headers for sorting; Notes column: =Number of Switches, =Number of Interactions)
Protein NameGene NameStartEndSubsequenceLogic#Ev.OrganismNotes
NMDZ1_HUMAN GRIN1 893 895 STLASSFKRRRSSKDTSTGG TP 5 Homo sapiens (Human)
1 
ABCC8_HUMAN ABCC8 648 651 AVPLRVVNRKRPAREDCRGL TP 5 Homo sapiens (Human)
IRK8_HUMAN KCNJ8 380 383 SELSHQNSLRKRNSMRRNNS TP 5 Homo sapiens (Human)
IRK11_HUMAN KCNJ11 368 371 TLASARGPLRKRSVPMAKAK TP 9 Homo sapiens (Human)
SCNAA_RAT Scn10a 495 497 SFLGLSSGRRRASHGSVFHF TP 4 Rattus norvegicus (Norway rat)
Q58F09_HUMAN GCS1 7 9 MARGERRRRAVPAEGVRTAE TP 2 Homo sapiens (Human)
ADA22_HUMAN ADAM22 851 854 KKKIRGKRFRPRSNSTETLS TP 4 Homo sapiens (Human)
1 
GPR15_HUMAN GPR15 352 354 LSTFIHAEDFARRRKRSVSL TP 6 Homo sapiens (Human)
1 
HG2A_HUMAN CD74 3 5 MHRRRSRSCREDQKPVMDDQ TP 4 Homo sapiens (Human)
1 
PAR4_HUMAN F2RL3 182 185 RYLALVHPLRARALRGRRLA TP 4 Homo sapiens (Human)
GABR1_HUMAN GABBR1 923 926 QLQSRQQLRSRRHPPTPPEP TP 3 Homo sapiens (Human)
1 
V2R_HUMAN AVPR2 247 249 GPSERPGGRRRGRRTGSPGE TP 3 Homo sapiens (Human)
GRIK5_HUMAN GRIK5 862 865 SCRKTSRSRRRRRPGGPSRA TP 5 Homo sapiens (Human)
GPAA1_HUMAN GPAA1 9 11 MGLLSDPVRRRALARLVLRL TN 3 Homo sapiens (Human)
PPLA_HUMAN PLN 12 14 VQYLTRSAIRRASTIEMPQQ TP 5 Homo sapiens (Human)
SGMR1_HUMAN SIGMAR1 7 9 MQWAVGRRWAWAALLLAVAA TP 3 Homo sapiens (Human)
SRPRB_HUMAN SRPRB 7 9 MASADSRRVADGGGAGGTFQ TP 3 Homo sapiens (Human)
SOAT1_HUMAN SOAT1 10 13 VGEEKMSLRNRLSKSRENPE TP 3 Homo sapiens (Human)
MSHR_HUMAN MC1R 160 163 YHSIVTLPRARRAVAAIWVA TP 4 Homo sapiens (Human)
C8ZIX9_YEAS8 EC 1118.1.2.2553g 8 11 MSLSLVSYRLRKNPWVNIFL TP 4 Saccharomyces cerevisiae EC1118
CFTR_HUMAN CFTR 553 556 GITLSGGQRARISLARAVYK FP 3 Homo sapiens (Human)
P2RX7_HUMAN P2RX7 575 578 AILPSCCRWRIRKEFPKSEG TP 2 Homo sapiens (Human)
SIAT9_MOUSE St3gal5 11 13 TEAVGGAARRPQKLRSQAAA TP 5 Mus musculus (House mouse)
S12A5_RAT Slc12a5 1101 1104 VLLNMPGPPRNRNGDENYME TP 2 Rattus norvegicus (Norway rat)
HMDH_NICSY HMGR 3 6 MDVRRRSEKPAYPTKEFAAG TP 1 Nicotiana sylvestris (Wood tobacco)
ADA10_HUMAN ADAM10 723 725 PLPGTLKRRRPPQPIQQPQR TP 4 Homo sapiens (Human)
NMDZ1_HUMAN GRIN1 893 895 STLASSFKRRRSSKDTQYHP TP 2 Homo sapiens (Human)
3 
Please cite: The Eukaryotic Linear Motif Resource ELM: 10 Years and Counting (PMID:24214962)

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