Casein kinase 2 reverses tail-independent inactivation of kinesin-1

Heterogeneous distribution of kinesin-streptavidin complexes revealed by Mass Photometry

Kinesin-streptavidin complexes are widely used in microtubule-based active-matter studies. The stoichiometry of the complexes is empirically tuned but experimentally challenging to determine. Here, mass photometry measurements reveal heterogenous distributions of kinesin-streptavidin complexes. Our binding model indicates that heterogeneity arises from both the kinesin-streptavidin mixing ratio and the kinesin-biotinylation efficiency.

Kinesin-1 autoinhibition facilitates the initiation of dynein cargo transport

The functional significance of Kinesin-1 autoinhibition has been unclear. Kinesin-1 transports multiple cargoes including cytoplasmic dynein to microtubule plus ends. From a genetic screen for Aspergillus mutants defective in dynein-mediated early endosome transport, we identified a kinesin-1 mutation kinAK895* at the C-terminal IAK motif involved in autoinhibition. The kinA∆IAK and kinAK895E mutants exhibited a similar defect in dynein-mediated early endosome transport, verifying the importance of kinesin-1 autoinhibition in dynein-mediated transport. Kinesin-1 autoinhibition is not critical for dynein accumulation at microtubule plus ends or for the secretory vesicle cargoes of kinesin-1 to reach the hyphal tip. However, it facilitates dynein to initiate early endosome transport. This is unrelated to a direct competition between dynein and kinesin-1 on early endosomes because kinesin-3 rather than kinesin-1 drives the plus-end-directed early endosome movement. This effect of kinesin-1 autoinhibition on dynein-mediated early endosome transport is related to cargo adapter-mediated dynein activation but at a step beyond the switching of dynein from its autoinhibited conformation.

Cholesterol in the cargo membrane amplifies tau inhibition of kinesin-1-based transport

Intracellular cargos are often membrane-enclosed and transported by microtubule-based motors in the presence of microtubule-associated proteins (MAPs). Whereas increasing evidence reveals how MAPs impact the interactions between motors and microtubules, critical questions remain about the impact of the cargo membrane on transport. Here we combined in vitro optical trapping with theoretical approaches to determine the effect of a lipid cargo membrane on kinesin-based transport in the presence of MAP tau. Our results demonstrate that attaching kinesin to a fluid lipid membrane reduces the inhibitory effect of tau on kinesin. Moreover, adding cholesterol, which reduces kinesin diffusion in the cargo membrane, amplifies the inhibitory effect of tau on kinesin binding in a dosage-dependent manner. We propose that reduction of kinesin diffusion in the cargo membrane underlies the effect of cholesterol on kinesin binding in the presence of tau, and we provide a simple model for this proposed mechanism. Our study establishes a direct link between cargo membrane cholesterol and MAP-based regulation of kinesin-1. The cholesterol effects uncovered here may more broadly extend to other lipid alterations that impact motor diffusion in the cargo membrane, including those associated with aging and neurological diseases.

The ubiquitous microtubule-associated protein 4 (MAP4) controls organelle distribution by regulating the activity of the kinesin motor

Regulation of organelle transport by molecular motors along the cytoskeletal microtubules is central to maintaining cellular functions. Here, we show that the ubiquitous tau-related microtubule-associated protein 4 (MAP4) can bias the bidirectional transport of organelles toward the microtubule minus-ends. This is concurrent with MAP4 phosphorylation, mediated by the kinase GSK3β. We demonstrate that MAP4 achieves this bias by tethering the cargo to the microtubules, allowing it to impair the force generation of the plus-end motor kinesin-1. Consistent with this mechanism, MAP4 physically interacts with dynein and dynactin and, when phosphorylated, associates with the cargo-motor complex through its projection domain. Its phosphorylation coincides with the perinuclear accumulation of organelles, a phenotype that is rescued by abolishing the cargo-microtubule MAP4 tether or by the pharmacological inhibition of dynein, confirming the ability of kinesin to inch along, albeit inefficiently, in the presence of phosphorylated MAP4. These findings have broad biological significance because of the ubiquity of MAP4 and the involvement of GSK3β in multiple diseases, more specifically in cancer, where the MAP4-dependent redistribution of organelles may be prevalent in cancer cells, as we demonstrate here for mitochondria in lung carcinoma epithelial cells.

A Journey through the Cytoskeleton with Protein Kinase CK2

Substrate pleiotropicity, a very acidic phosphorylation consensus sequence, and an apparent uncontrolled activity, are the main features of CK2, a Ser/Thr protein kinase that is required for a plethora of cell functions. Not surprisingly, CK2 appears to affect cytoskeletal structures and correlated functions such as cell shape, mechanical integrity, cell movement and division. This review outlines our current knowledge of how CK2 regulates cytoskeletal structures, and discusses involved pathways and molecular mechanisms.

MAP7 family proteins regulate kinesin-1 recruitment and activation

Kinesin-1 is responsible for microtubule-based transport of numerous cellular cargoes. Here, we explored the regulation of kinesin-1 by MAP7 proteins. We found that all four mammalian MAP7 family members bind to kinesin-1. In HeLa cells, MAP7, MAP7D1, and MAP7D3 act redundantly to enable kinesin-1-dependent transport and microtubule recruitment of the truncated kinesin-1 KIF5B-560, which contains the stalk but not the cargo-binding and autoregulatory regions. In vitro, purified MAP7 and MAP7D3 increase microtubule landing rate and processivity of kinesin-1 through transient association with the motor. MAP7 proteins promote binding of kinesin-1 to microtubules both directly, through the N-terminal microtubule-binding domain and unstructured linker region, and indirectly, through an allosteric effect exerted by the kinesin-binding C-terminal domain. Compared with MAP7, MAP7D3 has a higher affinity for kinesin-1 and a lower affinity for microtubules and, unlike MAP7, can be cotransported with the motor. We propose that MAP7 proteins are microtubule-tethered kinesin-1 activators, with which the motor transiently interacts as it moves along microtubules.

Phosphorylation of multiple sites within an acidic region of Alcadein α is required for kinesin-1 association and Golgi exit of Alcadein α cargo

Alcadein a (Alca) is reported to function as a cargo receptor when associated with kinesin-1. Phosphorylation of three serine residues in the acidic region located between the two WD motifs of Alca is required for interaction with kinesin-1 and Golgi exit of Alca cargo.

Alcadein α (Alcα) is a major cargo of kinesin-1 that is subjected to anterograde transport in neuronal axons. Two tryptophan- and aspartic acid-containing (WD) motifs located in its cytoplasmic domain directly bind the tetratricopeptide repeat (TPR) motifs of the kinesin light chain (KLC), which activate kinesin-1 and recruit kinesin-1 to Alcα cargo. We found that phosphorylation of three serine residues in the acidic region located between the two WD motifs is required for interaction with KLC. Phosphorylation of these serine residues may alter the disordered structure of the acidic region to induce direct association with KLC. Replacement of these serines with Ala results in a mutant that is unable to bind kinesin-1, which impairs exit of Alcα cargo from the Golgi. Despite this deficiency, the compromised Alcα mutant was still transported, albeit improperly by vesicles following missorting of the Alcα mutant with amyloid β-protein precursor (APP) cargo. This suggests that APP partially compensates for defective Alcα in anterograde transport by providing an alternative cargo receptor for kinesin-1.

Heterogeneity in kinesin function

The kinesin family proteins are often studied as prototypical molecular motors; a deeper understanding of them can illuminate regulation of intracellular transport. It is typically assumed that they function identically. Here we find that this assumption of homogeneous function appears incorrect: variation among motors' velocities in vivo and in vitro is larger than the stochastic variation expected for an ensemble of "identical" motors. When moving on microtubules, slow and fast motors are persistently slow, and fast, respectively. We develop theory that provides quantitative criteria to determine whether the observed single-molecule variation is too large to be generated from an ensemble of identical molecules. To analyze such heterogeneity, we group traces into homogeneous sub-ensembles. Motility studies varying the temperature, pH and glycerol concentration suggest at least 2 distinct functional states that are independently affected by external conditions. We end by investigating the functional ramifications of such heterogeneity through Monte-Carlo multi-motor simulations.

Native kinesin-1 does not bind preferentially to GTP-tubulin-rich microtubules in vitro

Molecular motors such as kinesin-1 work in small teams to actively shuttle cargos in cells, for example in polarized transport in axons. Here, we examined the potential regulatory role of the nucleotide state of tubulin on the run length of cargos carried by multiple kinesin motors, using an optical trapping-based in vitro assay. Based on a previous report that kinesin binds preferentially to GTP-tubulin-rich microtubules, we anticipated that multiple-kinesin cargos would run substantially greater distances along GMPCPP microtubules than along GDP microtubules. Surprisingly, we did not uncover any significant differences in run length between microtubule types. A combination of single-molecule experiments, comparison with previous theory, and classic microtubule affinity pulldown assays revealed that native kinesin-1 does not bind preferentially to GTP-tubulin-rich microtubules. The apparent discrepancy between our observations and the previous report likely reflects differences in post-translational modifications between the native motors used here and the recombinant motors examined previously. Future investigations will help shed light on the interplay between the motor's post-translational modification and the microtubule's nucleotide-binding state for transport regulation in vivo.

Lipid droplet functions beyond energy storage

Lipid droplets are cytoplasmic organelles that store neutral lipids and are critically important for energy metabolism. Their function in energy storage is firmly established and increasingly well characterized. However, emerging evidence indicates that lipid droplets also play important and diverse roles in the cellular handling of lipids and proteins that may not be directly related to energy homeostasis. Lipid handling roles of droplets include the storage of hydrophobic vitamin and signaling precursors, and the management of endoplasmic reticulum and oxidative stress. Roles of lipid droplets in protein handling encompass functions in the maturation, storage, and turnover of cellular and viral polypeptides. Other potential roles of lipid droplets may be connected with their intracellular motility and, in some cases, their nuclear localization. This diversity highlights that lipid droplets are very adaptable organelles, performing different functions in different biological contexts. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.

Quantitative Determination of the Probability of Multiple-Motor Transport in Bead-Based Assays

With their longest dimension typically being less than 100 nm, molecular motors are significantly below the optical-resolution limit. Despite substantial advances in fluorescence-based imaging methodologies, labeling with beads remains critical for optical-trapping-based investigations of molecular motors. A key experimental challenge in bead-based assays is that the number of motors on a bead is not well defined. Particularly for single-molecule investigations, the probability of single- versus multiple-motor events has not been experimentally investigated. Here, we used bead travel distance as an indicator of multiple-motor transport and determined the lower-bound probability of bead transport by two or more motors. We limited the ATP concentration to increase our detection sensitivity for multiple- versus single-kinesin transport. Surprisingly, for all but the lowest motor number examined, our measurements exceeded estimations of a previous model by ≥2-fold. To bridge this apparent gap between theory and experiment, we derived a closed-form expression for the probability of bead transport by multiple motors, and constrained the only free parameter in this model using our experimental measurements. Our data indicate that kinesin extends to ∼57 nm during bead transport, suggesting that kinesin exploits its conformational flexibility to interact with microtubules at highly curved interfaces such as those present for vesicle transport in cells. To our knowledge, our findings provide the first experimentally constrained guide for estimating the probability of multiple-motor transport in optical trapping studies. The experimental approach utilized here (limiting ATP concentration) may be generally applicable to studies in which molecular motors are labeled with cargos that are artificial or are purified from cellular extracts.

Microtubule Defects Influence Kinesin-Based Transport In Vitro

Microtubules are protein polymers that form "molecular highways" for long-range transport within living cells. Molecular motors actively step along microtubules to shuttle cellular materials between the nucleus and the cell periphery; this transport is critical for the survival and health of all eukaryotic cells. Structural defects in microtubules exist, but whether these defects impact molecular motor-based transport remains unknown. Here, we report a new, to our knowledge, approach that allowed us to directly investigate the impact of such defects. Using a modified optical-trapping method, we examined the group function of a major molecular motor, conventional kinesin, when transporting cargos along individual microtubules. We found that microtubule defects influence kinesin-based transport in vitro. The effects depend on motor number: cargos driven by a few motors tended to unbind prematurely from the microtubule, whereas cargos driven by more motors tended to pause. To our knowledge, our study provides the first direct link between microtubule defects and kinesin function. The effects uncovered in our study may have physiological relevance in vivo.

Single Molecule Investigation of Kinesin-1 Motility Using Engineered Microtubule Defects

The structure of the microtubule is tightly regulated in cells via a number of microtubule associated proteins and enzymes. Microtubules accumulate structural defects during polymerization, and defect size can further increase under mechanical stresses. Intriguingly, microtubule defects have been shown to be targeted for removal via severing enzymes or self-repair. The cell’s control in defect removal suggests that defects can impact microtubule-based processes, including molecular motor-based intracellular transport. We previously demonstrated that microtubule defects influence cargo transport by multiple kinesin motors. However, mechanistic investigations of the observed effects remained challenging, since defects occur randomly during polymerization and are not directly observable in current motility assays. To overcome this challenge, we used end-to-end annealing to generate defects that are directly observable using standard epi-fluorescence microscopy. We demonstrate that the annealed sites recapitulate the effects of polymerization-derived defects on multiple-motor transport, and thus represent a simple and appropriate model for naturally-occurring defects. We found that single kinesins undergo premature dissociation, but not preferential pausing, at the annealed sites. Our findings provide the first mechanistic insight to how defects impact kinesin-based transport. Preferential dissociation on the single-molecule level has the potential to impair cargo delivery at locations of microtubule defect sites in vivo.

CK2-An Emerging Target for Neurological and Psychiatric Disorders

Protein kinase CK2 has received a surge of attention in recent years due to the evidence of its overexpression in a variety of solid tumors and multiple myelomas as well as its participation in cell survival pathways. CK2 is also upregulated in the most prevalent and aggressive cancer of brain tissue, glioblastoma multiforme, and in preclinical models, pharmacological inhibition of the kinase has proven successful in reducing tumor size and animal mortality. CK2 is highly expressed in the mammalian brain and has many bona fide substrates that are crucial in neuronal or glial homeostasis and signaling processes across synapses. Full and conditional CK2 knockout mice have further elucidated the importance of CK2 in brain development, neuronal activity, and behavior. This review will discuss recent advances in the field that point to CK2 as a regulator of neuronal functions and as a potential novel target to treat neurological and psychiatric disorders.

Axonal Transport: A Constrained System

Long-distance intracellular axonal transport is predominantly microtubule-based, and its impairment is linked to neurodegeneration. Here we review recent theoretical and experimental evidence that suggest that near the axon boundaries (walls), the effective viscosity can become large enough to impede cargo transport in small (but not large) caliber axons. Theoretical work suggests that this opposition to motion increases rapidly as the cargo approaches the wall. However, having parallel microtubules close enough together to enable a cargo to simultaneously engage motors on more than one microtubule dramatically enhances motor activity, and thus decreases the effects due to such opposition. Experimental evidence supports this hypothesis: in small caliber axons, microtubule density is higher, increasing the probability of having parallel microtubules close enough that they can be used simultaneously by motors on a cargo. For transport toward the minus-end of microtubules, e.g., toward the cell body in an axon, a recently discovered force adaptation system can also contribute to overcoming such opposition to motion.

Load-induced enhancement of Dynein force production by LIS1-NudE in vivo and in vitro

Most sub-cellular cargos are transported along microtubules by kinesin and dynein molecular motors, but how transport is regulated is not well understood. It is unknown whether local control is possible, for example, by changes in specific cargo-associated motor behaviour to react to impediments. Here we discover that microtubule-associated lipid droplets (LDs) in COS1 cells respond to an optical trap with a remarkable enhancement in sustained force production. This effect is observed only for microtubule minus-end-moving LDs. It is specifically blocked by RNAi for the cytoplasmic dynein regulators LIS1 and NudE/L (Nde1/Ndel1), but not for the dynactin p150^Glued subunit. It can be completely replicated using cell-free preparations of purified LDs, where duration of LD force production is more than doubled. These results identify a novel, intrinsic, cargo-associated mechanism for dynein-mediated force adaptation, which should markedly improve the ability of motor-driven cargoes to overcome subcellular obstacles.

Transport of large cargo through the cytoplasm can encounter physical impediments which should be overcome. Here the authors show that lipid droplets constrained by an optical trap respond with an increase in dynein-mediated force that is dependent on dynein regulators LIS1 and NudE/L, but not on p150^glued.

JIP3 Activates Kinesin-1 Motility to Promote Axon Elongation

Kinesin-1 is a molecular motor responsible for cargo transport along microtubules and plays critical roles in polarized cells, such as neurons. Kinesin-1 can function as a dimer of two kinesin heavy chains (KHC), which harbor the motor domain, or as a tetramer in combination with two accessory light chains (KLC). To ensure proper cargo distribution, kinesin-1 activity is precisely regulated. Both KLC and KHC subunits bind cargoes or regulatory proteins to engage the motor for movement along microtubules. We previously showed that the scaffolding protein JIP3 interacts directly with KHC in addition to its interaction with KLC and positively regulates dimeric KHC motility. Here we determined the stoichiometry of JIP3-KHC complexes and observed approximately four JIP3 molecules binding per KHC dimer. We then determined whether JIP3 activates tetrameric kinesin-1 motility. Using an in vitro motility assay, we show that JIP3 binding to KLC engages kinesin-1 with microtubules and that JIP3 binding to KHC promotes kinesin-1 motility along microtubules. We tested the in vivo relevance of these findings using axon elongation as a model for kinesin-1-dependent cellular function. We demonstrate that JIP3 binding to KHC, but not KLC, is essential for axon elongation in hippocampal neurons as well as axon regeneration in sensory neurons. These findings reveal that JIP3 regulation of kinesin-1 motility is critical for axon elongation and regeneration.

Optical manipulation of single molecules in the living cell

Optical tweezers are the only nano-tools capable of manipulating and performing force-measurements on individual molecules and organelles within the living cell without performing destructive penetration through the cell wall and without the need for inserting a non-endogenous probe. Here, we describe how optical tweezers are used to manipulate individual molecules and perform accurate force and distance measurements within the complex cytoplasm of the living cell. Optical tweezers can grab individual molecules or organelles, if their optical contrast to the medium is large enough, as is the case, e.g., for lipid granules or chromosomes. However, often the molecule of interest is specifically attached to a handle manipulated by the optical trap. The most commonly used handles, their insertion into the cytoplasm, and the relevant micro-rheology of the cell are discussed here and we also review recent and exciting results achieved through optical force manipulation of individual molecules in vivo.

As the fat flies: The dynamic lipid droplets of Drosophila embryos

Research into lipid droplets is rapidly expanding, and new cellular and organismal roles for these lipid-storage organelles are continually being discovered. The early Drosophila embryo is particularly well suited for addressing certain questions in lipid-droplet biology and combines technical advantages with unique biological phenomena. This review summarizes key features of this experimental system and the techniques available to study it, in order to make it accessible to researchers outside this field. It then describes the two topics most heavily studied in this system, lipid-droplet motility and protein sequestration on droplets, discusses what is known about the molecular players involved, points to open questions, and compares the results from Drosophila embryo studies to what it is known about lipid droplets in other systems.

Calibration of optical tweezers for in vivo force measurements: how do different approaches compare?

There is significant interest in quantifying force production inside cells, but since conditions in vivo are less well controlled than those in vitro, in vivo measurements are challenging. In particular, the in vivo environment may vary locally as far as its optical properties, and the organelles manipulated by the optical trap frequently vary in size and shape. Several methods have been proposed to overcome these difficulties. We evaluate the relative merits of these methods and directly compare two of them, a refractive index matching method, and a light-momentum-change method. Since in vivo forces are frequently relatively high (e.g., can exceed 15 pN for lipid droplets), a high-power laser is employed. We discover that this high-powered trap induces local temperature changes, and we develop an approach to compensate for uncertainties in the magnitude of applied force due to such temperature variations.

A biophysical analysis of mitochondrial movement: differences between transport in neuronal cell bodies versus processes

There is an increasing interest in factors that can impede cargo transport by molecular motors inside the cell. Although potentially relevant (Yi JY, Ori-McKenney KM, McKenney RJ, Vershinin M, Gross SP, Vallee RB. High-resolution imaging reveals indirect coordination of opposite motors and a role for LIS1 in high-load axonal transport. J Cell Biol 2011;195:193-201), the importance of cargo size and subcellular location has received relatively little attention. Here we address these questions taking advantage of the fact that mitochondria - a common cargo - in Drosophila neurons exhibit a wide distribution of sizes. In addition, the mitochondria can be genetically marked with green fluorescent protein (GFP) making it possible to visualize and compare their movement in the cell bodies and in the processes of living cells. Using total internal reflection microscopy coupled with particle tracking and analysis, we quantified the transport properties of GFP-positive mitochondria as a function of their size and location. In neuronal cell bodies, we find little evidence for significant opposition to motion, consistent with a previous study on lipid droplets (Shubeita GT, Tran SL, Xu J, Vershinin M, Cermelli S, Cotton SL, Welte MA, Gross SP. Consequences of motor copy number on the intracellular transport of kinesin-1-driven lipid droplets. Cell 2008;135:1098-1107). However, in the processes, we observe an inverse relationship between the mitochondrial size and velocity and the run distances. This can be ameliorated via hypotonic treatment to increase process size, suggesting that motor-mediated movement is impeded in this more-confined environment. Interestingly, we also observe local mitochondrial accumulations in processes but not in cell bodies. Such accumulations do not completely block the transport but do increase the probability of mitochondria-mitochondria interactions. They are thus particularly interesting in relation to mitochondrial exchange of elements.

CK2 activates kinesin via induction of a conformational change

Kinesin is the canonical plus-end microtubule motor and has been the focus of intense study since its discovery in 1985. We previously demonstrated a time-dependent inactivation of kinesin in vitro that was fully reversible by the addition of purified casein kinase 2 (CK2) and showed that this inactivation/reactivation pathway was relevant in cells. Here we show that kinesin inactivation results from a conformational change that causes the neck linker to be positioned closer to the motor domain. Furthermore, we show that treatment of kinesin with CK2 prevents and reverses this repositioning. Finally, we demonstrate that CK2 treatment facilitates ADP dissociation from the motor, resulting in a nucleotide-free state that promotes microtubule binding. Thus, we propose that kinesin inactivation results from neck-linker repositioning and that CK2-mediated reactivation results from CK2's dual ability to reverse this repositioning and to promote ADP release.

Releasing the brake: restoring fast axonal transport in neurodegenerative disorders

Emerging evidence suggests that the dysregulation of fast axonal transport (FAT) plays a crucial role in several neurodegenerative disorders. Some of these diseases are caused by mutations affecting the molecular motors or adaptors that mediate FAT, and transport defects in organelles such as mitochondria and vesicles are observed in most, if not all neurodegenerative disorders. The relationship between neurodegenerative disorders and FAT is probably due to the extreme polarization of neurons, which extend long processes such as axons and dendrites. These characteristics render neurons particularly sensitive to transport alterations. Here we review the impact of such alterations on neuronal survival. We also discuss various strategies that might restore FAT, potentially slowing disease progression.

Endogenous GSK-3/shaggy regulates bidirectional axonal transport of the amyloid precursor protein

Neurons rely on microtubule (MT) motor proteins such as kinesin-1 and dynein to transport essential cargos between the cell body and axon terminus. Defective axonal transport causes abnormal axonal cargo accumulations and is connected to neurodegenerative diseases, including Alzheimer's disease (AD). Glycogen synthase kinase 3 (GSK-3) has been proposed to be a central player in AD and to regulate axonal transport by the MT motor protein kinesin-1. Using genetic, biochemical and biophysical approaches in Drosophila melanogaster, we find that endogenous GSK-3 is a required negative regulator of both kinesin-1-mediated and dynein-mediated axonal transport of the amyloid precursor protein (APP), a key contributor to AD pathology. GSK-3 also regulates transport of an unrelated cargo, embryonic lipid droplets. By measuring the forces motors generate in vivo, we find that GSK-3 regulates transport by altering the activity of kinesin-1 motors but not their binding to the cargo. These findings reveal a new relationship between GSK-3 and APP, and demonstrate that endogenous GSK-3 is an essential in vivo regulator of bidirectional APP transport in axons and lipid droplets in embryos. Furthermore, they point to a new regulatory mechanism in which GSK-3 controls the number of active motors that are moving a cargo.

Tuning multiple motor travel via single motor velocity

Microtubule-based molecular motors often work in small groups to transport cargos in cells. A key question in understanding transport (and its regulation in vivo) is to identify the sensitivity of multiple-motor-based motion to various single molecule properties. Whereas both single-motor travel distance and microtubule binding rate have been demonstrated to contribute to cargo travel, the role of single-motor velocity is yet to be explored. Here, we recast a previous theoretical study, and make explicit a potential contribution of velocity to cargo travel. We test this possibility experimentally, and demonstrate a strong negative correlation between single-motor velocity and cargo travel for transport driven by two motors. Our study thus discovers a previously unappreciated role of single-motor velocity in regulating multiple-motor transport.