关键区别 - Alpha Helix与Beta百褶片
Alpha helices and beta pleated sheets are the two most commonly found secondary structures in apolypeptidechain. These two structural components are the first main steps in the process of folding a polypeptide chain. Thekey difference在Alpha Helix和Beta Pleated床单之间结构体; they have two different shapes to do a specific job.
What is Alpha Helix?
An alpha helix is a right-handed coil of氨基酸多肽链上的残留物。氨基酸残基的范围可以从4到40个残基不等。这氢键formed between the oxygen of C=O group on the top coil and the hydrogen of the N-H group of the bottom coil help to hold the coil together. A hydrogen bond is formed per every four amino acid residues in the chain in the above manner. This uniform pattern gives it definite features such as the thickness of the coil and it dictates the length of each complete turn along the helix axis. The stability of alpha helix structure depends on several factors.
o红色的原子，蓝色的n原子和氢键为绿线
什么是Beta百褶床单？
Beta pleated sheet, also known as beta sheet, is considered as the second form of secondary structure in proteins. It contains beta strands which are connected laterally by a minimum of two or three backbone hydrogen bonds to form a twisted, pleated sheet as shown in the picture. A beta strand is a stretch of polypeptide chain; its length is generally equal to 3 to 10 amino acids, including backbone in an extended confirmation.
来自酶过氧化酶的晶体结构的4链反平行β片片段。
a) showing the antiparallel hydrogen bonds (dotted) between peptide NH and CO groups on adjacent strands. Arrows indicate chain direction, and electron density contours outline the non-H atoms. O atoms are red balls, N atoms are blue, and H atoms are omitted for simplicity; sidechains are shown only out to the first sidechain C atom (green)
b）中央两个β链的边缘视图
In beta pleated sheets, the polypeptide chains run alongside each other. It gets the name “pleated sheet” due to the wave-like appearance of the structure. They are linked together by hydrogen bonds. This structure allows forming more hydrogen bonds by stretching out the polypeptide chain.
Alpha Helix和Beta百褶床单有什么区别？
Structure of Alpha Helix and Beta Pleated Sheet
Alpha Helix:
In this structure, the polypeptide backbone is tightly bound around an imaginary axis as a spiral structure. It is also known as the helicoidal arrangement of the peptide chain.
这formation of alpha helix structure happens when the polypeptide chains are twisted into a spiral. This enables all the amino acids in the chain to form hydrogen bonds (a bonding between an oxygen molecule and a hydrogen molecule) with each other. The hydrogen bonds allow the helix to hold the spiral shape and gives a tight coil. This spiral shape makes the alpha helix very strong.
Hydrogen bonds are indicated by the yellow dots.
Beta Pleated Sheet:
When two or more fragments of polypeptide chain(s) overlap with one another, forming a row of hydrogen bonds with each other, following structures can be found. It can happen in two ways; parallel arrangement and anti-parallel arrangement.
Examples of the structure:
Alpha Helix:指甲或脚趾甲可以作为Alpha螺旋结构的一个例子。
Beta Pleated Sheet:羽毛的结构类似于β褶皱板的结构。
Features of the structure:
Alpha Helix:In alpha helix structure, there are 3.6 amino acids per turn of the helix. All thepeptide bonds是反式和平面，肽键中的N-H基团朝着相同的方向指向，该方向与螺旋的轴近似平行。所有肽键的C = O组指向相反的方向，它们与螺旋的轴平行。将每个肽键的C = O组键合成形成氢键的肽键的N-H组。所有R组都从螺旋中向外指向。
Beta Pleated Sheet:Beta折叠板中的每个肽键都是平面，具有反构形。来自相邻链的肽键的C = O和N-H组在同一平面，并彼此指向它们之间形成氢键。任何链中的所有R组都可以出现在纸板平面上方和下方。
Definitions:
次要结构：由于其骨架酰胺和羰基之间的氢键粘结而导致折叠蛋白的形状。
参考： “蛋白质结构”。ChemWiki: The Dynamic Chemistry Hypertext “Protein Secondary Structure: α-Helices and β-Sheets”。Proteinstructures.com by Salam Al Karadaghi “有机化学”。虚拟手机教科书 “Beta Sheet”.Wikipedia Image Courtesy: “Helix electron density myoglobin 2nrl 17-32” By Dcrjsr – Own work(CC BY 3.0)viaCommons Wikimedia EN：用户：Bikadi的“蛋白质二级结构”(CC BY-SA 3.0)viaCommons Wikimedia DCRJSR的“ 1GWE Antipar beta表” - 自己的作品(CC BY 3.0)viaCommons Wikimedia
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