Institute of Molecular Biophysics, Department of Biological Science, Florida State University, Tallahassee, 32306, USA.
Comp Biochem Physiol Part D Genomics Proteomics. 2011 Jun;6(2):171-7. doi: 10.1016/j.cbd.2011.02.004. Epub 2011 Mar 5.
The genome of the choanoflagellate Monosiga brevicollis contains at least three genes for the phosphoryl transfer enzyme, arginine kinase (AK; EC 2.7.3.3). Bioinformatic analyses of the deduced amino acid sequences of the proteins coded for by two of these genes showed that one of these AKs is cytoplasmic (denoted AK1) while the other appears to have an N-terminal mitochondrial targeting peptide (denoted AK2). Cloning and expression of the cDNA for AK1 yielded considerable soluble AK activity. Three AK2 constructs were expressed - one corresponding to the full length protein and two corresponding to truncated versions in which the signal peptide had been deleted. Expression of the former construct yielded minimal soluble activity. In contrast, significant AK activity was found in both truncated constructs confirming the importance of removal of the targeting peptide for proper folding and catalytic activity. Both AK1 and AK2 are functional oligomers unlike typical AKs which are monomeric. A phylogenetic analysis showed that these choanoflagellate AKs group more closely with a supercluster consisting of cytoplasmic and mitochondrial CKs and invertebrate AKs that evolved secondarily from a CK-like ancestor. Reaction-diffusion constraints in choanoflagellates are likely mitigated by the presence of AK isoforms which facilitate energy transport in these highly polarized cells.
具领虫 Monosiga brevicollis 的基因组至少包含三个磷酸转移酶精氨酸激酶（AK；EC 2.7.3.3）基因。对其中两个基因编码的蛋白质的推导氨基酸序列进行生物信息学分析表明，其中一个 AK 是细胞质的（表示为 AK1），而另一个似乎具有 N 端线粒体靶向肽（表示为 AK2）。AK1 的 cDNA 的克隆和表达产生了相当大的可溶性 AK 活性。表达了三个 AK2 构建体 - 一个对应于全长蛋白，两个对应于信号肽缺失的截断版本。前一个构建体的表达产生的可溶性活性最小。相比之下，在两个截断的构建体中都发现了显著的 AK 活性，这证实了去除靶向肽对于正确折叠和催化活性的重要性。AK1 和 AK2 都是功能性寡聚体，与典型的 AK 不同，典型的 AK 是单体。系统发育分析表明，这些领鞭毛虫 AK 与由细胞质和线粒体 CK 以及从 CK 样祖先进化而来的无脊椎动物 AK 组成的超簇关系更密切。具领鞭毛虫中的反应扩散限制可能通过存在 AK 同工型来缓解，这些同工型有利于这些高度极化细胞中的能量运输。
