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Definition

Cholecystokinin (CCK), also called pancreozymin, is a peptide hormone in the small intestine that constitutes the classical gut hormone triad together with gastrin and secretin1. CCK is secreted into the blood following ingestion of a meal and plays a critical role in the ingestion, absorption, intestinal motility, satiety signaling, inhibition of gastric acid secretion and digestion of food1.

Discovery

CCK was discovered in 1928 because of its ability to induce gallbladder contraction2.

Classification

CCK is a neuropeptide.  It is a family of hormones identified by the number of amino acids, for eg: CCK58 and CCK331. 

Structural Characteristics

Prepro-CCK is a115 amino acid peptide that is first cleaved to pro-CCK which in turn results in CCK58, the major processed form of CCK3.  CCK58 assumes a helix-turn-helix configuration3.

Mode of action

CCK binds to CCK receptors on the cell membrane that when activated increase the turnover of phosphatidyl inositol which results in the release of intracellular calcium4.  The calcium released causes increased enzyme secretion either directly or through activation of protein kinase C4.

Functions

CCK induces the gall bladder to contract and eject bile into the intestine5. It stimulates the acinar cells of the pancreas to release water and ions and stimulates the secretion of a juice rich in pancreatic digestive enzymes5. It is known to induce growth of the exocrine pancreas and to stimulate insulin secretion5. CCK is the most abundant neuropeptide in the human brain where it induces panic attacks that are antagonized by a central cholecystokinin receptor antagonist6. ProCCK is expressed in certain neuroendocrine tumors and sarcomas, and the secretion of CCK is impaired in celiac disease and bulimia nervosa7.

References

1.     Fink H, Rex A, Voits M, Voigt JP (1998). Major biological actions of CCK--a critical evaluation of research findings. Exp Brain Res., 123 (1-2), 77–83.

2.     Hunt, J. N. (1948). A method for estimating peptic activity in gastric contents. Biochem. J., 42, 104-109.

3.     Book: Neuropeptides By Fleur L. Strand, 387-389.

4.     Dufresne M, Seva C, Fourmy D (2006). Cholecystokinin and gastrin receptors. Physiol. Rev., 86 (3), 805–47.

5.     Chandra R, Liddle RA (2007). Cholecystokinin. Curr Opin Endocrinol Diabetes Obes., 14(1), 63-7.

6.     Rehfeld JF, Friis-Hansen L, Goetze JP, Hansen TV (2007). The biology of cholecystokinin and gastrin peptides. Curr Top Med Chem, 7(12), 1154-65.

7.     Rehfeld JF (2004). Clinical endocrinology and metabolism. Cholecystokinin. Best Pract Res Clin Endocrinol Metab., 18(4), 569-86.

多肽H2N-Asp-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe-Tyr-COOH的合成步骤：

1、合成CTC树脂：称取2.14g CTC Resin（如初始取代度约为1.18mmol/g）和3.03mmol Fmoc-Tyr(tBu)-OH于反应器中，加入适量DCM溶解氨基酸（需要注意，此时CTC树脂体积会增大好几倍，避免DCM溶液过少），再加入7.58mmol DIPEA（Mw：129.1,d：0.740g/ml），反应2-3小时后，可不抽滤溶液，直接加入1ml的HPLC级甲醇，封端半小时。依次用DMF洗涤2次，甲醇洗涤1次，DCM洗涤一次，甲醇洗涤一次，DCM洗涤一次，DMF洗涤2次（这里使用甲醇和DCM交替洗涤，是为了更好地去除其他溶质，有利于后续反应）。得到  Fmoc-Tyr(tBu)-CTC Resin。结构图如下：

2、脱Fmoc：加3倍树脂体积的20%Pip/DMF溶液，鼓氮气30分钟，然后2倍树脂体积的DMF 洗涤5次。得到 H2N-Tyr(tBu)-CTC Resin 。（此步骤脱除Fmoc基团，茚三酮检测为蓝色，Pip为哌啶）。结构图如下：

3、缩合：取7.58mmol Fmoc-Phe-OH 氨基酸，加入到上述树脂里，加适当DMF溶解氨基酸，再依次加入15.15mmol DIPEA，7.2mmol HBTU。反应30分钟后，取小样洗涤，茚三酮检测为无色。用2倍树脂体积的DMF 洗涤3次树脂。（洗涤树脂，去掉残留溶剂，为下一步反应做准备）。得到Fmoc-Phe-Tyr(tBu)-CTC Resin。氨基酸：DIPEA：HBTU：树脂=3：6：2.85：1（摩尔比）。结构图如下：

4、依次循环步骤二、步骤三，依次得到

H2N-Phe-Tyr(tBu)-CTC Resin

Fmoc-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin

H2N-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin

Fmoc-Met-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin

H2N-Met-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin

Fmoc-Trp(Boc)-Met-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin

H2N-Trp(Boc)-Met-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin

Fmoc-Gly-Trp(Boc)-Met-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin

H2N-Gly-Trp(Boc)-Met-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin

Fmoc-Met-Gly-Trp(Boc)-Met-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin

H2N-Met-Gly-Trp(Boc)-Met-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin

Fmoc-Asp(OtBu)-Met-Gly-Trp(Boc)-Met-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin

以上中间结构，均可在专肽生物多肽计算器-多肽结构计算器中，一键画出。

最后再经过步骤二得到 H2N-Asp(OtBu)-Met-Gly-Trp(Boc)-Met-Asp(OtBu)-Phe-Tyr(tBu)-CTC Resin，结构如下：

5、切割：6倍树脂体积的切割液（或每1g树脂加8ml左右的切割液），摇床摇晃 2小时，过滤掉树脂，用冰无水乙醚沉淀滤液，并用冰无水乙醚洗涤沉淀物3次，最后将沉淀物放真空干燥釜中，常温干燥24小试，得到粗品H2N-Asp-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe-Tyr-COOH。结构图见产品结构图。

切割液选择：1）TFA：H2O=95%：5%、TFA：H2O=97.5%：2.5%

2）TFA：H2O：TIS=95%：2.5%：2.5%

3）三氟乙酸：茴香硫醚：1，2-乙二硫醇：苯酚：水=87.5%：5%：2.5%：2.5%：2.5%

（前两种适合没有容易氧化的氨基酸，例如Trp、Cys、Met。第三种适合几乎所有的序列。）

6、纯化冻干：使用液相色谱纯化，收集目标峰液体，进行冻干，获得蓬松的粉末状固体多肽。不过这时要取小样复测下纯度 是否目标纯度。

7、最后总结：

杭州专肽生物技术有限公司（ALLPEPTIDE https://www.allpeptide.com）主营定制多肽合成业务，提供各类长肽，短肽，环肽，提供各类修饰肽，如：荧光标记修饰（CY3、CY5、CY5.5、CY7、FAM、FITC、Rhodamine B、TAMRA等），功能基团修饰肽（叠氮、炔基、DBCO、DOTA、NOTA等），同位素标记肽（N15、C13），订书肽（Stapled Peptide）,脂肪酸修饰肽（Pal、Myr、Ste），磷酸化修饰肽（P-Ser、P-Thr、P-Tyr），环肽（酰胺键环肽、一对或者多对二硫键环），生物素标记肽，PEG修饰肽，甲基化修饰肽

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