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Polo Boxes Come out of the Crypt: A New View of PLK Function and Evolution

2012; Elsevier BV; Volume: 20; Issue: 11 Linguagem: Inglês

10.1016/j.str.2012.10.008

1878-4186

Swadhin Chandra Jana, J. Fernando Bazán, Mónica Bettencourt‐Dias,

Cancer-related Molecular Pathways

Polo-like kinases (PLKs) are marked by C-terminal polo box modules with critical protein interaction and subcellular targeting roles. Slevin et al. in this issue of Structure reveal the architecture of a hidden set of polo boxes from the divergent PLK4, a critical player in centrosome duplication, shedding new light on the evolution of PLKs and their functionally related kinase ZYG-1. Polo-like kinases (PLKs) are marked by C-terminal polo box modules with critical protein interaction and subcellular targeting roles. Slevin et al. in this issue of Structure reveal the architecture of a hidden set of polo boxes from the divergent PLK4, a critical player in centrosome duplication, shedding new light on the evolution of PLKs and their functionally related kinase ZYG-1. Polo-like kinases (PLKs), well known for their multiple roles in interphase and mitosis, possess a characteristic modular architecture that joins an N-terminal kinase with a unique C-terminal structure called the polo box domain (PBD), which is comprised of a tandem set of ∼100 amino acid polo boxes (PB1 and PB2; Figure 1A). The PBD of PLK1 is involved in substrate binding, regulation of kinase activity, and localization at different subcellular structures and time points. It does so by binding to specific phosphorylated sequences on PLK1 substrates and regulators (reviewed in Archambault and Glover, 2009Archambault V. Glover D.M. Nat. Rev. Mol. Cell Biol. 2009; 10: 265-275Crossref PubMed Scopus (491) Google Scholar). SAK/PLK4 is the most divergent of all PLKs (Carvalho-Santos et al., 2010Carvalho-Santos Z. Machado P. Branco P. Tavares-Cadete F. Rodrigues-Martins A. Pereira-Leal J.B. Bettencourt-Dias M. J. Cell Sci. 2010; 123: 1414-1426Crossref PubMed Scopus (162) Google Scholar). This kinase localizes to centrosomes, is required for centrosome duplication, and abnormal protein levels are associated with tumorigenesis (reviewed in Brito et al., 2012Brito D.A. Gouveia S.M. Bettencourt-Dias M. Curr. Opin. Cell Biol. 2012; 24: 4-13Crossref PubMed Scopus (93) Google Scholar). The domain architecture of PLK4 appears distinct from PLK1-3; while PLK1 carries two PBs, PLK4 features only a divergent PB at its C terminus (hereafter called PB3; Figure 1A; Leung et al., 2002Leung G.C. Hudson J.W. Kozarova A. Davidson A. Dennis J.W. Sicheri F. Nat. Struct. Biol. 2002; 9: 719-724Crossref PubMed Scopus (121) Google Scholar). Comparison of the crystal structures of PLK1 PBD and the PLK4 PB3 surprisingly showed that they form different complexes in spite of a conserved modular fold, composed of a twisted antiparallel β sheet packed against a C-terminal helix. Whereas the tandem pair of PLK1 PBs form an intramolecular heterodimer (Figure 1B), the single PLK4 PB3 self-associates as an intermolecular, domain-swapped homodimer (Figure 1D) (Leung et al., 2002Leung G.C. Hudson J.W. Kozarova A. Davidson A. Dennis J.W. Sicheri F. Nat. Struct. Biol. 2002; 9: 719-724Crossref PubMed Scopus (121) Google Scholar; Elia et al., 2003Elia A.E. Rellos P. Haire L.F. Chao J.W. Ivins F.J. Hoepker K. Mohammad D. Cantley L.C. Smerdon S.J. Yaffe M.B. Cell. 2003; 115: 83-95Abstract Full Text Full Text PDF PubMed Scopus (604) Google Scholar; Cheng et al., 2003Cheng K.Y. Lowe E.D. Sinclair J. Nigg E.A. Johnson L.N. EMBO J. 2003; 22: 5757-5768Crossref PubMed Scopus (192) Google Scholar). Loss of PLK4 PB3 does not impair centrosome targeting or lead to complete loss of activity, suggesting the presence of other regulatory domains (Leung et al., 2002Leung G.C. Hudson J.W. Kozarova A. Davidson A. Dennis J.W. Sicheri F. Nat. Struct. Biol. 2002; 9: 719-724Crossref PubMed Scopus (121) Google Scholar; Brito et al., 2012Brito D.A. Gouveia S.M. Bettencourt-Dias M. Curr. Opin. Cell Biol. 2012; 24: 4-13Crossref PubMed Scopus (93) Google Scholar; Archambault and Glover, 2009Archambault V. Glover D.M. Nat. Rev. Mol. Cell Biol. 2009; 10: 265-275Crossref PubMed Scopus (491) Google Scholar). Interestingly, a centrally-located, conserved region in PLK4 was shown to dimerize and be sufficient for centrosome localization, and it was also required for PLK4 activity in centrosome formation (Leung et al., 2002Leung G.C. Hudson J.W. Kozarova A. Davidson A. Dennis J.W. Sicheri F. Nat. Struct. Biol. 2002; 9: 719-724Crossref PubMed Scopus (121) Google Scholar; Brito et al., 2012Brito D.A. Gouveia S.M. Bettencourt-Dias M. Curr. Opin. Cell Biol. 2012; 24: 4-13Crossref PubMed Scopus (93) Google Scholar; Slevin et al., 2012Slevin L.K. Nye J. Pinkerton D.C. Buster D.W. Rogers G.C. Slep K.C. Structure. 2012; 20 (this issue): 1905-1917Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar). These functional analogies to PBs gave rise to the cryptic polo box (CPB) label (Swallow et al., 2005Swallow C.J. Ko M.A. Siddiqui N.U. Hudson J.W. Dennis J.W. Oncogene. 2005; 24: 306-312Crossref PubMed Scopus (63) Google Scholar). Recently, PLK4 was suggested to be regulated by trans auto-phosphorylation within the dimer in a degron motif located N-terminal to the CPB domain (Guderian et al., 2010Guderian G. Westendorf J. Uldschmid A. Nigg E.A. J. Cell Sci. 2010; 123: 2163-2169Crossref PubMed Scopus (147) Google Scholar). Moreover, the CPB segment was shown to be essential for Asterless (Asl)/CEP152 binding and ensuing centrosome targeting (reviewed in Brito et al., 2012Brito D.A. Gouveia S.M. Bettencourt-Dias M. Curr. Opin. Cell Biol. 2012; 24: 4-13Crossref PubMed Scopus (93) Google Scholar). Solving the structure of the PLK4 CPB has become crucial for understanding the mechanisms of PLK4's mode of action and deciphering its relationship with the other PLKs. In this issue of Structure, Slevin et al., 2012Slevin L.K. Nye J. Pinkerton D.C. Buster D.W. Rogers G.C. Slep K.C. Structure. 2012; 20 (this issue): 1905-1917Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar present the crystal structure of the Drosophila PLK4 CPB at 2.3 Å resolution and reveal a pair of polo boxes, PB1 and PB2, that individually retain the distinctive fold of PLK1 PBs but lack the ∼15 residue linker between modules. As a result, the tightly fused CPB polo boxes adopt a head-to-tail packing arrangement (Figure 1C), which dramatically differs from the side-by-side placement of the PLK1 PBs (Figure 1B), or the intertwined homodimer of PLK4 PB3s (Figure 1D). Furthermore, the authors also found that PLK4 CPB forms a stable pseudosymmetric homodimer along its length, clustering their respective N-termini (Slevin et al., 2012Slevin L.K. Nye J. Pinkerton D.C. Buster D.W. Rogers G.C. Slep K.C. Structure. 2012; 20 (this issue): 1905-1917Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar). Adding to previous findings in Drosophila and human cells (reviewed in Brito et al., 2012Brito D.A. Gouveia S.M. Bettencourt-Dias M. Curr. Opin. Cell Biol. 2012; 24: 4-13Crossref PubMed Scopus (93) Google Scholar), the CPB cassette is required for binding the centriolar protein Asl in vivo and centriole targeting (Slevin et al., 2012Slevin L.K. Nye J. Pinkerton D.C. Buster D.W. Rogers G.C. Slep K.C. Structure. 2012; 20 (this issue): 1905-1917Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar). Moreover, the CPB is also necessary to ensure proper PLK4 degradation (Slevin et al., 2012Slevin L.K. Nye J. Pinkerton D.C. Buster D.W. Rogers G.C. Slep K.C. Structure. 2012; 20 (this issue): 1905-1917Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar). The arrangement of PBs in the CPB illustrates the unusual plasticity of binary PB interactions that create modular scaffolds with potentially distinct binding and oligomerization functions. For instance, the two PLK1 PBs and the three PLK4 PBs demonstrate four different organizational modes (Figures 1B–1D and 2A ): (1) the PBD of PLK1 (composed of PB1 and PB2), (2) the CPB of PLK4 (PB1 and PB2), (3) the dimer interface of the CPBs of PLK4, and (4) the domain-swapped dimer of PLK4 PB3s (Leung et al., 2002Leung G.C. Hudson J.W. Kozarova A. Davidson A. Dennis J.W. Sicheri F. Nat. Struct. Biol. 2002; 9: 719-724Crossref PubMed Scopus (121) Google Scholar; Slevin et al., 2012Slevin L.K. Nye J. Pinkerton D.C. Buster D.W. Rogers G.C. Slep K.C. Structure. 2012; 20 (this issue): 1905-1917Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar). The distinct PB packing modes imposed on the PLK1 PBD and PLK4 CPB by their respective tether lengths has the effect in the former structure of creating a β sheet-protected pocket that binds a Ser/Thr-phosphopeptide chain by a β strand addition mechanism to the N-terminal edge of the PB1 module β sheet. By contrast, the PBs of the CPB create a groove at their modular interface, which is an attractive protein binding site (where the PB1 module of the CPB could also employ a β strand recognition scheme) for interactors, such as Asl, and still undefined substrates (Figures 1C and 2D; Slevin et al., 2012Slevin L.K. Nye J. Pinkerton D.C. Buster D.W. Rogers G.C. Slep K.C. Structure. 2012; 20 (this issue): 1905-1917Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar); the absence of a phosphate-recognition cavity in the CPB groove argues that protein binding might be phospho-independent (Slevin et al., 2012Slevin L.K. Nye J. Pinkerton D.C. Buster D.W. Rogers G.C. Slep K.C. Structure. 2012; 20 (this issue): 1905-1917Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar). The PB3 domain plays a dimerization role in PLK4 by contributing to an extensive dimer interface (Figures 1D and 2A), and we speculate that it may also seed the formation of higher-order scaffolds by inter-dimer linking of PB3 modules (Figure 2C). These complexes could, for example, have a structural role in centriole assembly, as recently shown for oligomers of SAS6 that template the 9-fold symmetrical cartwheel structure of centrioles (Figure 2C) (reviewed in Brito et al., 2012Brito D.A. Gouveia S.M. Bettencourt-Dias M. Curr. Opin. Cell Biol. 2012; 24: 4-13Crossref PubMed Scopus (93) Google Scholar). The addition of CPB to the collection of PB folds expands our view of the structural and functional plasticity of this protein module, which is proving more versatile than other interaction modules tethered to kinase domains (Jin and Pawson, 2012Jin J. Pawson T. Philos. Trans. R. Soc. Lond. B Biol. Sci. 2012; 367: 2540-2555Crossref PubMed Scopus (108) Google Scholar). The CPB notably stabilizes the PLK4 dimer and juxtaposes the kinase domains, which facilitates the trans autophosphorylation of both degrons. Simultaneously, the CPB creates a binding platform for globular substrates like Asl (Figures 2B and 2D). The precise mutational ablation of the different dimer interfaces in PLK4 will drive a better understanding of how PLK4 function is regulated as both a catalytic entity and architectural scaffold. PLK4s are the outliers of the PLK family, as judged by their greater divergence of both kinase domains and PB arrays (Carvalho-Santos et al., 2010Carvalho-Santos Z. Machado P. Branco P. Tavares-Cadete F. Rodrigues-Martins A. Pereira-Leal J.B. Bettencourt-Dias M. J. Cell Sci. 2010; 123: 1414-1426Crossref PubMed Scopus (162) Google Scholar). As Slevin et al.'s work now demonstrates, the architecture of the CPB (coupled to the oligomerizing PB3 domain) provides the PLK4 kinase with a unique scaffolding ability absent in the other PLKs and sets PLK4 functionally apart as an enzymatic and perhaps also structural component of the centriole (Figure 2). A PLK4 ortholog has not been detected in the C. elegans genome (Carvalho-Santos et al., 2010Carvalho-Santos Z. Machado P. Branco P. Tavares-Cadete F. Rodrigues-Martins A. Pereira-Leal J.B. Bettencourt-Dias M. J. Cell Sci. 2010; 123: 1414-1426Crossref PubMed Scopus (162) Google Scholar). There is an intriguing molecule, ZYG-1, that operationally fits the mold of an active PLK4, including how it is degraded, but its kinase domain lies on a distal branch of the kinome tree from PLKs and is thought to be a case of functional convergence (Carvalho-Santos et al., 2010Carvalho-Santos Z. Machado P. Branco P. Tavares-Cadete F. Rodrigues-Martins A. Pereira-Leal J.B. Bettencourt-Dias M. J. Cell Sci. 2010; 123: 1414-1426Crossref PubMed Scopus (162) Google Scholar, Peel et al., 2012Peel N. Dougherty M. Goeres J. Liu Y. O'Connell K.F. J. Cell Sci. 2012; 125: 3535-3544Crossref PubMed Scopus (23) Google Scholar). However, the featureless 435 residues following the ZYG-1 kinase domain are rich in predicted secondary structure, and, using sensitive fold recognition methods (Bazan and de Sauvage, 2009Bazan J.F. de Sauvage F.J. Cell. 2009; 138: 1055-1056Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar) focused on this C-terminal globular region of ZYG-1, we can predict the presence of a PLK4-like array of CPB and PB3 domains (Figure 1E). If the CPB and PB3 are vital to this PLK4-like outlier, then perhaps ZYG-1 is an unorthodox PLK4 whose kinase sequence has evolutionarily drifted more rapidly than the main PLK4 branch, obscuring its true orthology. PLK4 phylogeny is presently limited to fungi and animals (Carvalho-Santos et al., 2010Carvalho-Santos Z. Machado P. Branco P. Tavares-Cadete F. Rodrigues-Martins A. Pereira-Leal J.B. Bettencourt-Dias M. J. Cell Sci. 2010; 123: 1414-1426Crossref PubMed Scopus (162) Google Scholar); it will be important to investigate the divergence of CPB and PBD domains in order to further understand PLK4's evolutionary origins and its function in centriole biogenesis. We apologize to colleagues whose work was not discussed or cited owing to space constraints. We thank Inês Cunha-Ferreira, Zita Carvalho-Santos, Tiago M. Bandeiras, Gregory C. Rogers, Jose Pereira-Leal, and Sihem Zitouni for critically reading the manuscript. S.C.J. and M.B.D. are funded by an EMBO Installation grant (cofunded by FCT and Instituto Gulbenkian de Ciência) and the EMBO YIP Program, (FP7/2010)/ERC Grant "261344-CentrioleStructNumber," and Fundação para a Ciência e Tecnologia (FCT) "PTDC/BIA-BCM/105602/2008". The Structure of the Plk4 Cryptic Polo Box Reveals Two Tandem Polo Boxes Required for Centriole DuplicationSlevin et al.StructureSeptember 20, 2012In BriefPolo like kinase 4 (Plk4) is a centriole duplication factor that localizes to centrioles via the Cryptic Polo Box (PB) domain. Slevin et al. present the structure of this domain, revealing asymmetric PB1-PB2 homodimer, required for centriole targeting and trans-autophosphorylation that primes Plk4 for degradation. Full-Text PDF Open ArchivePolo Boxes Come out of the Crypt: A New View of PLK Function and EvolutionJana et al.StructureDecember 05, 2012In Brief(Structure 20, 1801–1804, November 2, 2012) Full-Text PDF Open Archive