The Eukaryotic Linear Motif resource for
Functional Sites in Proteins
Functional site class:
Polyproline profilin-binding motif
Functional site description:
Profilin is a key regulator of the cytoskeleton due to its actin-binding and filament-inducing activity. Solved structures of profilin (2PAV, 2V8C and 2V8F) show that it bears a groove to accept short poly-proline sequence motifs with seven or eight residues making contact. A sequence with at least five prolines is required for the binding although they do not all need to be consecutive (Ferron,2007). The peptide prolines make hydrophobic interactions with amino acids in the profilin pocket while the peptide backbone provides H-bonds that precisely position the peptide. Profilin does not act alone but cooperates with other actin filament promoting proteins. These include Mena, Ena/VASP, mDia1, CAPPUCCINO, Bni1p, cdc12, formin and WASF1. In formins, the profilin-binding region is known as FH1 and contains multiple profilin binding sites. Most proteins that bind profilin through Pro-motifs are likely to be able to bind multiple profilin molecules.
ELM Description:
The surface of profilin has a hydrophobic groove which accepts a Pro-rich motif (2PAV, 2V8C). Tyr3, Trp6, Trp31 and His139 are involved in the binding of the Pro-rich motifs and are conserved in the sequences of different eukaryotic organisms from Homo sapiens to Acanthamoeba; His139 is sometimes replaced by Phe (Mahoney,1997).
The ELM motif pattern spans seven residues. The first five residues of the motif are the most conserved with positions 6-7 being more variable. Proline at the +4 position (2V8C; 2V8F) can be replaced by Alanine (PDB :2PAV): Proline at + 4 inserts inside the groove and it is stacked against the aromatic chains of the residues lining the groove; Alanine, when present at +4, shows the same orientation and it is extremely conserved among different species from Homo sapiens to both Xenopus laevis and coelacanth (Latimeria). Kursula and collaborators (Kursula,2008) superimposed two different sequences that bind into the groove and they reported that the second, the third and the fourth Proline of IPPPPPLP (O08808, 635-642) have an orientation comparable with the third, the fourth and the fifth proline of GPPPPPGPPPPP (P70460, 167-174). Backbone oxygens at +1 and +4 form H-bonds to Profilin: For example, in mDIAP these residues form H-bonds with Trp3 and Tyr6. Leucine is a frequently observed residue either at position +6 or +7. This residue is found also in WASF1 and not only determines the polarity of the interaction but also is responsible for the orientation of the peptides (Ferron,2007). The ELM pattern finds most of the Pro-rich repeats in the profilin-binding regions but may miss some which have a rarer Pro substitution.
Pattern: PPP[PA]P((P[LGP])|([LG]P))
Pattern Probability: 4.881e-07
Present in taxon: Eukaryota
Interaction Domain:
Profilin (PF00235) Profilin (Stochiometry: 1 : 1)
o See 16 Instances for LIG_PROFILIN_1
o Abstract
Profilin (PF00235) is an abundant predominantly cytosolic protein that possesses an actin-binding activity (7758455;Ferron,2007) whereby it regulates the actin cytoskeleton; therefore, it is involved in many different biological processes ranging from cadherin binding (7758455) to actin-based mobility of pathogenic Listeria (9204886). In Homo sapiens there are two genes on chromosome 17, named PFN1 and PFN2, that code for two proteins (P07737 and P35080) having the same function even though the protein sequence is slightly different, as noted by the isoelectric point (pI) shows (pI (P07737 = 8.4; pI P35080 = 5.9)(7758455). The surface of profilins has two grooves, one required for actin binding and the other for binding proline-rich peptides (2PAV; 2V8C).
Actin polymerization is the process responsible for the formation of microfilaments. Each microfilament consists of a number of actin polymers plus other accessory proteins. Microfilaments are required for different functions from endocytosis/exocytosis to muscular contraction.
Several properties allow profilin to be a key regulator of the actin polymerization process. In particular, at high concentrations, it maintains actin in an unpolymerized status while it enhances the aforementioned process at low concentration (7758455); it binds different cytoskeletal proteins such as Ena/VASP (Kursula,2008) or Arp2/3. Profilin’s role in actin filament regulation is always undertaken cooperatively with sets of other proteins. The first step is called ‘actin nucleation’ and it sees the formation of an actin core initiated with three actin monomers from which a new actin filament will elongate. Among proteins that initiate nucleus formation, a major role is played by formins, a family of proteins that have a strong conserved C-terminal Formin Homology-2 (FH2) domain with an upstream formin homology-1 (FH1) domain. FH1 contains the Pro-rich profilin-binding motifs while FH2 interacts with monomers of globular actin (G-actin) and initiates nucleation. Higashida et al. (15044801) reported that mDia1, a member of the formin family, accelerates the actin nucleation rate and it associates with the barbed end of growing actin filament.
Enabled/Vasodilator-stimulated phosphoprotein (Ena/VASP) is another major protein in filament elongation requiring preformed F-actin to initiate further elongation. Ena/VASP contains different domains: N-terminal EVH1 domains, a Pro-rich domain and a C-terminal EVH2 domain (Siton-Mendelson,2017). Furthermore, the proline-rich domain could be split into three subdomains: a regulatory site, a recruiting domain which includes multiple repeats of the GPPPPP sequence and a “loading poly-Pro site”, which is required to deliver the profilin-actin complex from the poly-Pro region to the globular-actin-binding domain (GAB) of VASP (Ferron,2007). The proline-rich domain is responsible for the profilin-VASP interaction (Kursula,2008). The ability of VASP to promote actin filament elongation depends on its capability to recruit G-actin monomers and include them in the newly synthesized filament.
Profilin regulation of actin cytoskeletal organization is also involved in neurulation and commissure formation. Axonal growth responds to multiple cues present in the extracellular environment and this response triggers a signaling response which affect the cytoskeletal structures (26783725). Mammalian enabled (Mena) is a VASP family protein thought to be the linker between the signaling input and actin cytoskeleton remodelling. It is reported that Mena interacts with profilin thanks to a proline-rich segment (10069337) and Mena-deficient mice show abnormalities in the brain and die in utero.
Profilin interactions were also reported in Insects (Manseau,1996) and Fungi (Chang,1997;Evangelista,1997). In Drosophila, CAPPUCCINO (Q24120) interacts with profilin during embryonic development (Manseau,1996); in Saccharomyces cerevisiae Bni1pa yeast formin, associates with profilin and in Schizosaccharomyces pombe the complex cdc12p-profilin plays a key role during cell division (Mahoney,1997). All these proteins have Pro-rich motifs but the profilin interactions were only tested at whole protein level.
Intracellular pathogens need to control the actin cytoskeleton and several bacterial effector proteins are known to contain short motifs involved in actin filament regulation. Although no bacterial profilin-binding motif has been reported yet, several bacterial proteins functionally mimic profilin-interacting proteins to infect the host cells: for instance the organisms Burkholderia pseudomallei, Listeriamonocytogenes and Rickettsia (Siton-Mendelson,2017). The BimA effector of Burkholderia seems to mimic the function of VASP as it is also capable of nucleating actin (Benanti,2015) and has a long poly-Proline sequence thought likely to bind profilin. Bacteria from the genus Listeria use actin filaments as a sort of trail to move into the cell they have infected (9204886). The entire process requires ActA, a bacterial protein that is exposed on the cell surface, and cellular VASP, which interacts with ActA, and, in turn, tethers profilin to promote actin polymerization.
o 8 selected references:

o 7 GO-Terms:

o 16 Instances for LIG_PROFILIN_1
(click table headers for sorting; Notes column: =Number of Switches, =Number of Interactions)
Acc., Gene-, NameStartEndSubsequenceLogic#Ev.OrganismNotes
Q10059 cdc12
948 954 PAFPPPPPPPPPLVSAAGGK TP 1 Schizosaccharomyces pombe 972h-
P41832 BNI1
1285 1291 APPPPPPPPPPPPMALFGKP TP 1 Saccharomyces cerevisiae S288c
Q24120 capu
520 526 LANYGAPPPPPPPPPGSGSA TP 1 Drosophila melanogaster (Fruit fly)
Q24120 capu
507 513 PPPPPPPPPPPPPLANYGAP TP 1 Drosophila melanogaster (Fruit fly)
Q24120 capu
488 494 AVAPPPPPPPPPLHAFVAPP TP 1 Drosophila melanogaster (Fruit fly)
Q92558 WASF1
326 332 VSPTPPPPPPPLPSALSTSS TP 2 Homo sapiens (Human)
O08808 Diaph1
697 703 PGSVGVPPPPPLPGGPGLPP TP 1 Mus musculus (House mouse)
O08808 Diaph1
685 691 GGTGIPPPPPPLPGSVGVPP TP 1 Mus musculus (House mouse)
O08808 Diaph1
672 678 PGATAIPPPPPLPGGTGIPP TP 1 Mus musculus (House mouse)
O08808 Diaph1
660 666 PGATAIPPPPPLPGATAIPP TP 1 Mus musculus (House mouse)
O08808 Diaph1
612 618 PPGTCIPPPPPLPGGACIPP TP 1 Mus musculus (House mouse)
O08808 Diaph1
589 595 TVIPPPPPPPPLPGGVVPPS TP 1 Mus musculus (House mouse)
O08808 Diaph1
648 654 PGVASIPPPPPLPGATAIPP TP 5 Mus musculus (House mouse)
O08808 Diaph1
636 642 PGSAAIPPPPPLPGVASIPP TP 5 Mus musculus (House mouse)
P70460 Vasp
166 172 APPAGGPPPPPGPPPPPGPP TP 4 Mus musculus (House mouse)
P50552 VASP
204 210 HGAGGGPPPAPPLPAAQGPG TP 3 Homo sapiens (Human)
Please cite: The Eukaryotic Linear Motif resource: 2022 release. (PMID:34718738)

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