Recombinant proteins were often expressed with His-tag to simplify the purification process. Among them, transaminase was mostly expressed with fusion tags and widely used in the production of numerous amino moieties. However, the existence of the His-tag has been reported to affect various properties of different recombinant enzymes, while the effect on transaminase was rarely studied. In this paper, we investigated the effect of His-tag on transaminase based on the various activities of 4-aminobutyrate-2-oxoglutarate transaminase (GabT) when it was expressed in vector pETDuet-1. We found that His-tag did not affect the enantioselectivity, but decreased the catalytic activity to different extents according to its existence and location. Native GabT maintained the highest catalytic activity; GabT with C-terminal His-tag showed slightly lower activity than native GabT but about 2.2-fold higher than GabT with N-terminal His-tag. Besides, other fusion tags like T7-tag and S-tag inserted between N-His-tag and GabT can relieve the decreasing effect of His-tag on GabT activity. Furthermore, whole cell catalytic activity of several transaminases was improved by deleting the N-terminal His-tag. This study provided a strategy for the efficient expression of recombinant transaminase with improved catalytic activity and might attract attention to the effect of His-tag on other enzymatic properties.

中文翻译：

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His标签对重组转氨酶的催化活性和对映选择性的影响。

重组蛋白经常与His标签一起表达，以简化纯化过程。其中，转氨酶主要用融合标签表达，并广泛用于产生大量氨基。然而，据报道，His-标签的存在会影响不同重组酶的各种特性，而对转氨酶的影响却很少被研究。在本文中，我们基于4-氨基丁酸-2-氧代谷氨酸转氨酶（GabT）在载体pETDuet-1中表达时的各种活性，研究了His-tag对转氨酶的影响。我们发现，His-tag不会影响对映选择性，但会根据其存在和位置在不同程度上降低催化活性。天然的GabT保持最高的催化活性。具有C末端His-tag的GabT的活性略低于天然GabT，但比具有N末端His-tag的GabT高约2.2倍。此外，在N-His标签和GabT之间插入T7标签和S标签等其他融合标签可以缓解His标签对GabT活性的降低作用。此外，通过删除N端His-tag，提高了几种转氨酶的全细胞催化活性。这项研究提供了一种有效表达重组转氨酶并提高催化活性的策略，并且可能引起人们对His-tag对其他酶性质的影响的关注。通过删除N端His-tag可提高几种转氨酶的全细胞催化活性。这项研究提供了一种有效表达重组转氨酶并提高催化活性的策略，并且可能引起人们对His-tag对其他酶性质的影响的关注。通过删除N端His-tag可提高几种转氨酶的全细胞催化活性。这项研究提供了一种有效表达重组转氨酶并提高催化活性的策略，并且可能引起人们对His-tag对其他酶性质的影响的关注。