Moriarty D F, Raleigh D P
Department of Chemistry, State University of New York at Stony Brook 11794-3400, USA.
Biochemistry. 1999 Feb 9;38(6):1811-8. doi: 10.1021/bi981658g.
Amylin, also known as islet amyloid polypeptide (IAPP), is the major protein component of the fibril deposits found in the pancreas of individuals with type II diabetes. The central region of amylin, residues 20-29, has been implicated as a key determinate of amyloid formation. To establish which positions are most important for amyloid formation, the wild-type sequence of the 20-29 fragment and a set of 10 variants have been synthesized in which a proline was placed at each position. Proline is energetically unfavorable in the extended cross-beta structure found in amyloid. If a particular position is critical for amyloid formation, then substitution with a proline should inhibit amyloid formation. A proline substitution at any position inhibited aggregation and amyloid formation. Substitution of Asn22, Gly24, and residues 26-28 had the largest effect. Fourier transform infrared (FTIR) spectroscopy showed little secondary structure in these peptides, and transmission electron microscopy (TEM) showed mostly amorphous material. The peptides were much more soluble than the wild-type sequence, and no birefringence was observed with Congo Red staining. Proline substitutions at the N (residues 20 and 21) and C termini showed the least effect. These peptides showed the classic fibril morphology, a significant amount of beta-sheet structure, and exhibited green birefringence when stained with Congo Red. The results indicate that residues 22, 24, and 26-28 play a key role in formation of amyloid by amylin. Positions 23 and 25 also appear to be important, but may be less critical than positions 22, 24, and 26-28.
胰淀素，也被称为胰岛淀粉样多肽（IAPP），是在II型糖尿病患者胰腺中发现的纤维沉积物的主要蛋白质成分。胰淀素的中央区域，即第20 - 29位氨基酸残基，被认为是淀粉样蛋白形成的关键决定因素。为了确定哪些位置对淀粉样蛋白形成最为重要，已合成了20 - 29片段的野生型序列以及一组10种变体，其中在每个位置都引入了脯氨酸。在淀粉样蛋白中发现的延伸交叉β结构中，脯氨酸在能量上是不利的。如果某个特定位置对淀粉样蛋白形成至关重要，那么用脯氨酸替代应该会抑制淀粉样蛋白的形成。在任何位置进行脯氨酸替代都会抑制聚集和淀粉样蛋白的形成。Asn22、Gly24以及第26 - 28位氨基酸残基的替代效果最为显著。傅里叶变换红外（FTIR）光谱显示这些肽几乎没有二级结构，透射电子显微镜（TEM）显示大多为无定形物质。这些肽比野生型序列的溶解性高得多，刚果红染色未观察到双折射现象。在N端（第20和21位氨基酸残基）和C端进行脯氨酸替代的效果最小。这些肽呈现出典型的纤维形态，有大量的β折叠结构，用刚果红染色时呈现绿色双折射。结果表明，第22、24以及26 - 28位氨基酸残基在胰淀素形成淀粉样蛋白的过程中起关键作用。第23和25位氨基酸残基似乎也很重要，但可能不如第22、24以及26 - 28位氨基酸残基那么关键。
