探討醣化反應對胰島類澱粉蛋白聚集的影響
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2018
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蛋白質醣化反應是指環境中醣分子的羰基與蛋白質的胺基進行反應，使胺基酸側鏈醣基化的過程，這種非酵素轉譯後修飾的反應可能會造成蛋白質結構上與穩定性的改變。近年來許多研究指出蛋白質醣化反應在許多疾病中扮演重要的角色，例如: 糖尿病併發症、骨骼相關疾病和神經退行性疾病(阿茲海默症、帕金森氏症)。這些疾病有一共通點即是類澱粉蛋白形成不可溶物堆積在器官周圍或者隨著血液流至身體各部位。在過去幾年中，有許多在體內發現的醣化最終產物其結構已慢慢被檢測與鑑定出來。儘管如此，醣化反應對於蛋白質聚集的影響仍尚未明瞭。目前已有研究指出在超過95%第二型糖尿病患的體內發現了胰島類澱粉蛋白不正常的聚集進而影響胰島功能，使胰島素分泌下降。在本研究中，我們想了解醣化過程對蛋白質聚集的影響及其醣化後的胰島類澱粉蛋白對正常的胰島類澱粉蛋白聚集的影響。因此，藉由胜肽合成儀將醣化修飾後的胺基酸合成到蛋白質序列中，透過這個方式模擬胺基酸在高濃度的血糖中可能發生的改變。研究顯示出醣化後的胰島類澱粉蛋白形成類澱粉蛋白纖維的速度較胰島類澱粉蛋白快速，並生成較高分子量的聚集物。接著透過圓偏光二色性圖譜發現醣化後的胰島類澱粉蛋白的結構從原先不定型結構轉換成摺疊纖維結構的速度也較胰島類澱粉蛋白來的快速。此外，也發現醣化後的胰島類澱粉蛋白可以誘導胰島類澱粉蛋白的聚集，並且透過核誘發實驗推測醣化後的胰島類澱粉蛋白的核種可以做為一個模板促進胰島類澱粉蛋白快速聚集。透過染料滲漏試驗發現醣化後的胰島類澱粉蛋白與胰島類澱粉蛋白皆可與合成的脂囊泡作用推測其亦具有破壞細胞膜的能力。由以上的研究結果我們可以得知醣化的修飾對於胰島類澱粉蛋白有加速形成類澱粉蛋白纖維的能力，並且可能對於第二型糖尿病的進展有很大的影響。
Protein glycation refers to the process in which the carbonyl group of sugars react with the amine group of proteins to form glycated proteins. This non-enzymatic posttranslational modification may change the structure and stability of the protein. In recent years, many studies have pointed out that protein glycation plays an important role in many diseases, such as diabetic complication, bone-related diseases, and neurodegenerative diseases (Alzheimer’s disease and Parkinson’s disease). One of the common features of these diseases is that the amyloid accumulates around the organ as the insoluble form or through the body via bloodstream. In the past years, the structure of many advanced glycation end-products (AGEs) has been detected and identified in vivo. However, the effect of glycation on protein aggregation is unclear. In addition, many studies have shown that islet amyloid polypeptide (IAPP) was found to form islet amyloid in over 95% of patients with type 2 diabetes (T2D), and it affects the function of islet and results in reducing the secretion of the insulin. In this study, we would like to investigate the influence of glycation on IAPP aggregation. Therefore, we synthesized AGE-IAPP by changing the sturcutre of Lys side chain to commonly identified AGEs, carboxymethylysine (CML), to mimic the consequence of the peptide in the hyperglycemia (high blood sugar) environment. Our study showed that AGE-IAPP formed amyloid fibril faster than IAPP and accompanied with the higher molecular weight aggregates. Next, from circular dichroism spectra, we found that the structure of AGE-IAPP converted from random coil to β-sheet fibril state at a faster rate than IAPP. Furthermore, we found that AGE-IAPP could induce IAPP aggregation. And seeding experiments also indicated the seeds of AGE-IAPP could act as a template to promote IAPP aggregation quickly. Besides, dye leakage assay indicated that both of AGE-IAPP and IAPP have the ability to interact with the synthetic membranes. As the result, we demonstrated that the glycation modification has the ability to accelerate the amyloid formation of IAPP, and may have a great impact on the progression of T2D.
Protein glycation refers to the process in which the carbonyl group of sugars react with the amine group of proteins to form glycated proteins. This non-enzymatic posttranslational modification may change the structure and stability of the protein. In recent years, many studies have pointed out that protein glycation plays an important role in many diseases, such as diabetic complication, bone-related diseases, and neurodegenerative diseases (Alzheimer’s disease and Parkinson’s disease). One of the common features of these diseases is that the amyloid accumulates around the organ as the insoluble form or through the body via bloodstream. In the past years, the structure of many advanced glycation end-products (AGEs) has been detected and identified in vivo. However, the effect of glycation on protein aggregation is unclear. In addition, many studies have shown that islet amyloid polypeptide (IAPP) was found to form islet amyloid in over 95% of patients with type 2 diabetes (T2D), and it affects the function of islet and results in reducing the secretion of the insulin. In this study, we would like to investigate the influence of glycation on IAPP aggregation. Therefore, we synthesized AGE-IAPP by changing the sturcutre of Lys side chain to commonly identified AGEs, carboxymethylysine (CML), to mimic the consequence of the peptide in the hyperglycemia (high blood sugar) environment. Our study showed that AGE-IAPP formed amyloid fibril faster than IAPP and accompanied with the higher molecular weight aggregates. Next, from circular dichroism spectra, we found that the structure of AGE-IAPP converted from random coil to β-sheet fibril state at a faster rate than IAPP. Furthermore, we found that AGE-IAPP could induce IAPP aggregation. And seeding experiments also indicated the seeds of AGE-IAPP could act as a template to promote IAPP aggregation quickly. Besides, dye leakage assay indicated that both of AGE-IAPP and IAPP have the ability to interact with the synthetic membranes. As the result, we demonstrated that the glycation modification has the ability to accelerate the amyloid formation of IAPP, and may have a great impact on the progression of T2D.
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醣化最終產物, 胰島類澱粉蛋白, 蛋白質聚集, 第二型糖尿病, Advanced glycation end-products, aggregation, islet amyloid polypeptide, type 2 diabetes