NMT1 and NMT2 are lysine myristoyltransferases regulating the ARF6 GTPase cycle

At the beginning of the budding yeast cell cycle, the GTPase Cdc42p promotes the assembly of a ring of septins at the site of future bud emergence. Here, we present an analysis of cdc42 mutants that display specific defects in septin organization, which identifies an important role for GTP hydrolysis by Cdc42p in the assembly of the septin ring. The mutants show defects in basal or stimulated GTP hydrolysis, and the septin misorganization is suppressed by overexpression of a Cdc42p GTPase-activating protein (GAP). Other mutants known to affect GTP hydrolysis by Cdc42p also caused septin misorganization, as did deletion of Cdc42p GAPs. In performing its roles in actin polarization and transcriptional activation, GTP-Cdc42p is thought to function by activating and/or recruiting effectors to the site of polarization. Excess accumulation of GTP-Cdc42p due to a defect in GTP hydrolysis by the septin-specific alleles might cause unphysiological activation of effectors, interfering with septin assembly. However, the recessive and dose-sensitive genetic behavior of the septin-specific cdc42 mutants is inconsistent with the septin defect stemming from a dominant interference of this type. Instead, we suggest that assembly of the septin ring involves repeated cycles of GTP loading and GTP hydrolysis by Cdc42p. These results suggest that a single GTPase, Cdc42p, can act either as a ras-like GTP-dependent “switch” to turn on effectors or as an EF-Tu–like “assembly factor” using the GTPase cycle to assemble a macromolecular structure.

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Receptor compaction and GTPase rearrangement drive SRP-mediated cotranslational protein translocation into the ER

Science Advances ◽

10.1126/sciadv.abg0942 ◽

2021 ◽

Vol 7 (21) ◽

pp. eabg0942

Author(s):

Jae Ho Lee ◽

Ahmad Jomaa ◽

SangYoon Chung ◽

Yu-Hsien Hwang Fu ◽

Ruilin Qian ◽

...

Keyword(s):

Single Molecule ◽

Protein Translocation ◽

Molecular Model ◽

Genetic Diseases ◽

Signal Recognition Particle ◽

Biological Regulation ◽

Single Molecule Studies ◽

Guanosine Triphosphatase ◽

Gtpase Cycle

The conserved signal recognition particle (SRP) cotranslationally delivers ~30% of the proteome to the eukaryotic endoplasmic reticulum (ER). The molecular mechanism by which eukaryotic SRP transitions from cargo recognition in the cytosol to protein translocation at the ER is not understood. Here, structural, biochemical, and single-molecule studies show that this transition requires multiple sequential conformational rearrangements in the targeting complex initiated by guanosine triphosphatase (GTPase)–driven compaction of the SRP receptor (SR). Disruption of these rearrangements, particularly in mutant SRP54G226E linked to severe congenital neutropenia, uncouples the SRP/SR GTPase cycle from protein translocation. Structures of targeting intermediates reveal the molecular basis of early SRP-SR recognition and emphasize the role of eukaryote-specific elements in regulating targeting. Our results provide a molecular model for the structural and functional transitions of SRP throughout the targeting cycle and show that these transitions provide important points for biological regulation that can be perturbed in genetic diseases.

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Stochastic simulation of the transducin GTPase cycle

Biophysical Journal ◽

10.1016/s0006-3495(96)79499-7 ◽

1996 ◽

Vol 71 (6) ◽

pp. 3051-3063 ◽

Cited By ~ 26

Author(s):

S. Felber ◽

H.P. Breuer ◽

F. Petruccione ◽

J. Honerkamp ◽

K.P. Hofmann

Keyword(s):

Stochastic Simulation ◽

Gtpase Cycle

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Deregulated expression of the RanBP1 gene alters cell cycle progression in murine fibroblasts

Journal of Cell Science ◽

10.1242/jcs.110.19.2345 ◽

1997 ◽

Vol 110 (19) ◽

pp. 2345-2357 ◽

Cited By ~ 1

Author(s):

A. Battistoni ◽

G. Guarguaglini ◽

F. Degrassi ◽

C. Pittoggi ◽

A. Palena ◽

...

Keyword(s):

Cell Cycle ◽

Dna Replication ◽

Cell Cycle Progression ◽

Protein Import ◽

Proliferating Cells ◽

Cycle Progression ◽

Ran Gtpase ◽

Genes Encoding ◽

Active Transcription ◽

Gtpase Cycle

RanBP1 is a molecular partner of the Ran GTPase, which is implicated in the control of several processes, including DNA replication, mitotic entry and exit, cell cycle progression, nuclear structure, protein import and RNA export. While most genes encoding Ran-interacting partners are constitutively active, transcription of the RanBP1 mRNA is repressed in non proliferating cells, is activated at the G1/S transition in cycling cells and peaks during S phase. We report here that forced expression of the RanBP1 gene disrupts the orderly execution of the cell division cycle at several stages, causing inhibition of DNA replication, defective mitotic exit and failure of chromatin decondensation during the telophase-to-interphase transition in cells that achieve nuclear duplication and chromosome segregation. These results suggest that deregulated RanBP1 activity interferes with the Ran GTPase cycle and prevents the functioning of the Ran signalling system during the cell cycle.

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Ran GTPase Cycle and Importins α and β Are Essential for Spindle Formation and Nuclear Envelope Assembly in LivingCaenorhabditis elegans Embryos

Molecular Biology of the Cell ◽

10.1091/mbc.e02-06-0346 ◽

2002 ◽

Vol 13 (12) ◽

pp. 4355-4370 ◽

Cited By ~ 127

Author(s):

Peter Askjaer ◽

Vincent Galy ◽

Eva Hannak ◽

Iain W. Mattaj

Keyword(s):

Nuclear Envelope ◽

Cell Function ◽

Small Gtpase ◽

Spindle Formation ◽

Ran Gtpase ◽

Early Embryos ◽

Nuclear Envelope Assembly ◽

Importin Α ◽

Gtpase Cycle

The small GTPase Ran has been found to play pivotal roles in several aspects of cell function. We have investigated the role of the Ran GTPase cycle in spindle formation and nuclear envelope assembly in dividing Caenorhabditis elegans embryos in real time. We found that Ran and its cofactors RanBP2, RanGAP, and RCC1 are all essential for reformation of the nuclear envelope after cell division. Reducing the expression of any of these components of the Ran GTPase cycle by RNAi leads to strong extranuclear clustering of integral nuclear envelope proteins and nucleoporins. Ran, RanBP2, and RanGAP are also required for building a mitotic spindle, whereas astral microtubules are normal in the absence of these proteins. RCC1(RNAi) embryos have similar abnormalities in the initial phase of spindle formation but eventually recover to form a bipolar spindle. Irregular chromatin structures and chromatin bridges due to spindle failure were frequently observed in embryos where the Ran cycle was perturbed. In addition, connection between the centrosomes and the male pronucleus, and thus centrosome positioning, depends upon the Ran cycle components. Finally, we have demonstrated that both IMA-2 and IMB-1, the homologues of vertebrate importin α and β, are essential for both spindle assembly and nuclear formation in early embryos.

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Membrane curvature and the control of GTP hydrolysis in Arf1 during COPI vesicle formation

Biochemical Society Transactions ◽

10.1042/bst0330619 ◽

2005 ◽

Vol 33 (4) ◽

pp. 619-622 ◽

Cited By ~ 24

Author(s):

B. Antonny ◽

J. Bigay ◽

J.-F. Casella ◽

G. Drin ◽

B. Mesmin ◽

...

Keyword(s):

Lipid Membranes ◽

Membrane Curvature ◽

Gtp Hydrolysis ◽

Membrane Fission ◽

Transport Vesicles ◽

Highly Sensitive ◽

Copi Vesicle ◽

Membrane Budding ◽

Gtpase Cycle ◽

Adp Ribosylation Factor

The GTP switch of the small G-protein Arf1 (ADP-ribosylation factor 1) on lipid membranes promotes the polymerization of the COPI (coat protein complex I) coat, which acts as a membrane deforming shell to form transport vesicles. Real-time measurements for coat assembly on liposomes gives insights into how the GTPase cycle of Arf1 is coupled in time with the polymerization of the COPI coat and the resulting membrane deformation. One key parameter seems to be the membrane curvature. Arf-GAP1 (where GAP stands for GTPase-activating protein), which promotes GTP hydrolysis in the Arf1–COPI complex is highly sensitive to lipid packing. Its activity on Arf1-GTP increases by two orders of magnitude as the diameter of the liposomes approaches that of authentic transport vesicles (60 nm). This suggests that during membrane budding, Arf1-GTP molecules are progressively eliminated from the coated area where the membrane curvature is positive, but are protected from Arf-GAP1 at the bud neck due to the negative curvature of this region. As a result, the coat should be stable as long as the bud remains attached and should disassemble as soon as membrane fission occurs.

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Conserved charged residues in the leucine-rich repeat domain of the Ran GTPase activating protein are required for Ran binding and GTPase activation

Biochemical Journal ◽

10.1042/bj3430653 ◽

1999 ◽

Vol 343 (3) ◽

pp. 653-662 ◽

Cited By ~ 12

Author(s):

Jörg HABERLAND ◽

Volker GERKE

Keyword(s):

Nucleocytoplasmic Transport ◽

Small Gtpases ◽

Structural Basis ◽

Ran Gtpase ◽

Protein Protein Interaction ◽

Charged Residues ◽

Gtpase Activation ◽

Gtpase Cycle ◽

Leucine Rich Repeats ◽

Lrr Domain

GTPase activating proteins (GAPs) for Ran, a Ras-related GTPase participating in nucleocytoplasmic transport, have been identified in different species ranging from yeast to man. All RanGAPs are characterized by a conserved domain consisting of eight leucine-rich repeats (LRRs) interrupted at two positions by so-called separating regions, the latter being unique for RanGAPs within the family of LRR proteins. The cytosolic RanGAP activity is essential for the Ran GTPase cycle which in turn provides directionality in nucleocytoplasmic transport, but the structural basis for the interaction between Ran and its GAP has not been elucidated. In order to gain a better understanding of this interaction we generated a number of mutant RanGAPs carrying amino acid substitutions in the LRR domain and analysed their complex formation with Ran as well as their ability to stimulate the intrinsic GTPase activity of the G protein. We show that conserved charged residues present in the separating regions of the LRR domain are indispensable for efficient Ran binding and GAP activity. These separating regions contain three conserved arginines which could possibly serve as catalytic residues similar to the arginine fingers identified in GAPs for other small GTPases. However, mutations in two of these arginines do not affect the GAP activity and replacement of the third conserved arginine (Arg91 in human RanGAP) severely interferes not only with GAP activity but also with Ran binding. This indicates that RanGAP-stimulated GTP hydrolysis on Ran does not involve a catalytic arginine residue but requires certain charged residues of the LRR domain of the GAP for mediating the protein-protein interaction.

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A GTPase Cycle Coupled to the Cell Cycle

The Cell Cycle ◽

10.1007/978-1-4615-2421-2_11 ◽

1994 ◽

pp. 99-110

Author(s):

Elias Coutavas ◽

Mindong Ren ◽

Joel D. Oppenheim ◽

Vijay Yajnik ◽

Peter D’Eustachio ◽

...

Keyword(s):

Cell Cycle ◽

Gtpase Cycle

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Accumulation of rab4GTP in the Cytoplasm and Association with the Peptidyl-Prolyl Isomerase Pin1 during Mitosis

Molecular Biology of the Cell ◽

10.1091/mbc.11.7.2201 ◽

2000 ◽

Vol 11 (7) ◽

pp. 2201-2211 ◽

Cited By ~ 27

Author(s):

Lisya Gerez ◽

Karin Mohrmann ◽

Marcel van Raak ◽

Mandy Jongeneelen ◽

Xiao Zhen Zhou ◽

...

Keyword(s):

Membrane Transport ◽

Subcellular Fractionation ◽

Effector Proteins ◽

Endocytic Pathway ◽

Prolyl Isomerase ◽

Peptidyl Prolyl Isomerase ◽

Transport Vesicles ◽

Early Endosomes ◽

Gtpase Cycle ◽

Mitotic Cells

Transport through the endocytic pathway is inhibited during mitosis. The mechanism responsible for this inhibition is not understood. Rab4 might be one of the proteins involved as it regulates transport through early endosomes, is phosphorylated by p34cdc2 kinase, and is translocated from early endosomes to the cytoplasm during mitosis. We investigated the perturbation of the rab4 GTPase cycle during mitosis. Newly synthesized rab4 was less efficiently targeted to membranes during mitosis. By subcellular fractionation of mitotic cells, we found a large increase of cytosolic rab4 in the active GTP-form, an increase not associated with the cytosolic rabGDP chaperone GDI. Instead, phosphorylated rab4 is in a complex with the peptidyl-prolyl isomerase Pin1 during mitosis, but not during interphase. Our results show that less efficient recruitment of rab4 to membranes and a bypass of the normal GDI-mediated retrieval of rab4GDP from early endosomes reduce the amount of rab4GTP on membranes during mitosis. We propose that phosphorylation of rab4 inhibits both the recruitment of rab4 effector proteins to early endosomes and the docking of rab4-containing transport vesicles. This mechanism might contribute to the inhibition of endocytic membrane transport during mitosis.

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