Urade Y, Oberdick J, Molinar-Rode R, Morgan J I
Department of Neurosciences, Roche Institute of Molecular Biology, Nutley, NJ 07110.
Proc Natl Acad Sci U S A. 1991 Feb 1;88(3):1069-73. doi: 10.1073/pnas.88.3.1069.
The cerebellum contains a hexadecapeptide, termed cerebellin, that is conserved in sequence from human to chicken. Three independent, overlapping cDNA clones have been isolated from a human cerebellum cDNA library that encode the cerebellin sequence. The longest clone codes for a protein of 193 amino acids that we term precerebellin. This protein has a significant similarity (31.3% identity, 52.2% similarity) to the globular (non-collagen-like) region of the B chain of human complement component C1q. The region of relatedness extends over approximately 145 amino acids located in the carboxyl terminus of both proteins. Unlike C1q B chain, no collagen-like motifs are present in the amino-terminal regions of precerebellin. The amino terminus of precerebellin contains three possible N-linked glycosylation sites. Although hydrophobic amino acids are clustered at the amino terminus, they do not conform to the classical signal-peptide motif, and no other obvious membrane-spanning domains are predicted from the cDNA sequence. The cDNA predicts that the cerebellin peptide is flanked by Val-Arg and Glu-Pro residues. Therefore, cerebellin is not liberated from precerebellin by the classical dibasic amino acid proteolytic-cleavage mechanism seen in many neuropeptide precursors. In Northern (RNA) blots, precerebellin transcripts, with four distinct sizes (1.8, 2.3, 2.7, and 3.0 kilobases), are abundant in cerebellum. These transcripts are present at either very low or undetectable levels in other brain areas and extraneural structures. A similar pattern of cerebellin precursor transcripts are seen in rat, mouse, and human cerebellum. Furthermore, a partial genomic fragment from mouse shows the same bands in Northern blots as the human cDNA clone. During rat development, precerebellin transcripts mirror the level of cerebellin peptide. Low levels of precerebellin mRNA are seen at birth. Levels increase modestly from postpartum day 1 to 8, then increase more dramatically between day 5 and 15, and eventually reach peak values between day 21 and 56. Because cerebellin-like immunoreactivity is associated with Purkinje cell postsynaptic structures, these data raise interesting possibilities concerning the function of the cerebellin precursor in synaptic physiology.
小脑含有一种十六肽，称为小脑素，其序列在人类到鸡之间是保守的。已从人小脑cDNA文库中分离出三个独立的、重叠的cDNA克隆，它们编码小脑素序列。最长的克隆编码一种193个氨基酸的蛋白质，我们称之为前小脑素。该蛋白质与人补体成分C1q B链的球状（非胶原样）区域具有显著相似性（31.3%的同一性，52.2%的相似性）。相关区域延伸至两种蛋白质羧基末端约145个氨基酸。与C1q B链不同，前小脑素的氨基末端不存在胶原样基序。前小脑素的氨基末端含有三个可能的N-连接糖基化位点。虽然疏水氨基酸聚集在氨基末端，但它们不符合经典的信号肽基序，并且从cDNA序列中预测不出其他明显的跨膜结构域。cDNA预测小脑素肽两侧是Val-Arg和Glu-Pro残基。因此，小脑素不是通过许多神经肽前体中所见的经典双碱性氨基酸蛋白水解切割机制从前小脑素中释放出来的。在Northern（RNA）印迹中，前小脑素转录本有四种不同大小（1.8、2.3、2.7和3.0千碱基），在小脑中含量丰富。这些转录本在其他脑区和神经外结构中含量极低或无法检测到。在大鼠、小鼠和人小脑中观察到类似的小脑素前体转录本模式。此外，来自小鼠的部分基因组片段在Northern印迹中显示出与人类cDNA克隆相同的条带。在大鼠发育过程中，前小脑素转录本反映了小脑素肽的水平。出生时前小脑素mRNA水平较低。从产后第1天到第8天水平适度增加，然后在第5天到第15天之间增加更为显著，最终在第21天到第56天之间达到峰值。由于小脑素样免疫反应性与浦肯野细胞突触后结构相关，这些数据为小脑素前体在突触生理学中的功能提出了有趣的可能性。
