UNC-104/KIF1A是一種具有神經專一性的分子馬達，於神經軸突的微管上移動，主要功能為運輸軸突中的突觸囊泡。然而，如何調控UNC-104其方向性運輸特性的分子機制尚未被完全了解。近期的研究指出UNC-104所攜帶的貨物(如突觸前驅物)能夠調控分子馬達的運動。例如active zone蛋白 SYD-2能夠促進UNC-104往anterograde的方向移動。SYD-2 會與UNC-104的特定區域coiled-coil結合，我們研究其他的文獻發現另一個蛋白LIN-2也會與這個區域結合，因此，我們推測LIN-2可能也會參與UNC-104的調控機制。LIN-2屬於一個蛋白質家族: membrane-associated guanylate kinase (MAGUK)家族，它在哺乳類中的同源蛋白為CASK，CASK是由許多特殊區堿構成的鷹架蛋白(multidomain scaffolding protein)且在神經中的表現量特別高。有趣的是，在之前的研究中發現UNC-104具有一個MAGUK蛋白的結合位(MAGUK binding stalk, MBS)，而我們的酵母菌雙雜合實驗的確顯示UNC-104的MBS會與LIN-2的GUK區域結合。另一個有趣的發現為LIN-2ΔGUK雖然無法與UNC-104的MBS結合，卻會和UNC-104的FHA-CC2有很強的交互作用，有些研究發現FHA-CC2可能會負向地調控馬達的活性。此外，LIN-2的SH3-GUK被視為一個功能性單元，我們的實驗顯示SH3-GUK對於LIN-2 與UNC-104 的MBS結合是有抑制性的，然而，SH3-GUK卻與FHA-CC2有很強的交互作用。除了in vitro的探討，我們也發現在lin-2 基因被剔除的秀麗隱桿線蟲中，UNC-104往anterograde方向移動的能力受到影響 (anterograde移動路徑變短)，而往retrograde方向的運輸(由另一個分子馬達dynein負責)卻被提昇了(retrograde速度變快)。這些數據顯示，在沒有LIN-2蛋白的情況下，UNC-104與dynein間類似拔河的競爭現象受到影響，UNC-104較容易輸給dynein，造成UNC-104往anterograde方向的運輸能力減弱，而由dynein負責往retrograde方向的運輸則被提昇。這些結果顯示了LIN-2所扮演的新角色:與UNC-104進行交互作用並且活化UNC-104的運動能力。

UNC-104/KIF1A is microtubule-dependent, neuron-specific kinesin responsible for fast axonal transport of synaptic vesicles. However, the molecular mechanism of regulating UNC-104 directional transport is not fully understood. Recent studies suggest that cargo as synaptic precursors could regulate the motor’s movements. For example, the active zone proteins SYD-2 was found to facilitate UNC-104’s motility in anterograde directions. SYD-2 binds to a specific domain at the motor’s coiled-coil region and reviewing the literature we found that another protein LIN-2 also binds to this region, therefore this protein might be also involved in motor regulation. LIN-2 is a member of the membrane-associated guanylate kinase (MAGUK) family, and its mammalian homologue of LIN-2 is CASK, multidomain scaffolding protein highly expressed in neurons. Interestingly, a previous study revealed that UNC-104 contains a MBS (MAGUK binding stalk) site, and indeed, our yeast two-hybrid assay showed that a MBS construct of UNC-104 interacts with LIN-2’s GUK domain. Interestingly, a LIN-2ΔGUK construct reveals reduced interaction with UNC-104’s MBS, but strong interaction with UNC-104’s FHA-CC2 domain, suggesting to negatively regulate the motor’s activity. In addition, the integrated SH3-GUK unit may be inhibitory for LIN-2’s interaction with the MBS while on the other hand it strongly interacts with the FHA-CC2 domain. Besides these in vitro investigations, we found that in lin-2 knockout worms, the anterograde transport of UNC-104 is reduced (displaying e.g. shorter run-lengths), while the retrograde transport (carried out by the dynein motor) is enhanced. These data implicate that loss-of-function of LIN-2 causes UNC-104 to suffer defeat in tug-of-war events between opposing motors, resulting in impaired anterograde but facilitated retrograde transport. Together, these data demonstrate a novel role for LIN-2 to directly interact with UNC-104 and to activate the motor’s motility.

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