CONSTRAINING BETA-TURN STRUCTURE IN MODEL IMMUNOGENS

球状蛋白质分子主要由β折叠和α折叠组成。 螺旋状二级结构由链轨迹的急剧变化分开 在分子表面上的四个残基β-转角或更大的环处。 这些betaturn和环结构通常可以在蛋白质中识别 序列，有助于二级结构预测和 抗体潜在线性肽表位的鉴定 生产而识别完整蛋白质的抗肽抗体 链已经在许多情况下制备，所产生的单克隆 抗体通常对折叠的蛋白质具有低亲和力， 合成肽免疫原序列。提出了一项协议， 使用第二种蛋白质（葡萄球菌核酸酶）作为“宿主”， 通过将“客体”肽免疫原掺入天然结构中， 序列在适当位点处插入杂合蛋白。工作将继续 在两个杂交蛋白质系统上开发这种方法，并了解其 在结构和物理方面的成功或失败。 过去三年的结果表明， 序列和β-转弯类型之间的关系， 相对于球状蛋白背景效应显性。调查将 继续定义氨基酸序列与 β-转弯类型。这些实验应该能改善我们的 预测球状蛋白中betaturn位点的能力，并应定义 上述杂合蛋白的蛋白质工程设计原理， 其他新的蛋白质分子。核磁共振和X射线晶体学 实验将继续努力，以确定物理基础， 其中顺式肽键在VI型β-转角中是有利的， 葡萄球菌核酸酶该系统提供了一个观察 氨基酸序列对两个β-转角平衡的影响 在球状蛋白质的表面。遗传学和晶体学 分析将继续定义与I'型一致的序列 核酸酶中的β-转折，以及这些的物理和结构基础 序列偏好。

Globular protein molecules are largely composed of beta-sheet and alpha- helical secondary structures separated by sharp changes in chain trajectory at four residue beta-turns or larger loops on the surface of the molecule. These betaturn and loop structures can often be recognized in protein sequences, aiding in secondary structure prediction and in the identification of potential linear peptide epitopes for antibody production. While antipeptide antibodies which recognize a full protein chain have been prepared in a number of cases, the resulting monoclonal antibodies often have a low affinity for the folded protein from which the synthetic peptide immunogen sequence was derived. A protocol was proposed to use a second protein (staphylococcal nuclease) as a "host" to constrain the "guest" peptide immunogen into a native structure by incorporating that sequence into a hybrid protein at an appropriate site. Work will continue on two hybrid protein systems to develop this method and to understand its success or failure in structural and physical terms. Results during the last three years indicate that there is a strong relationship between the sequence and type of a beta-turn which can be dominant over globular protein context effects. Investigations will continue to define the relationship between amino acid sequence and beta-turn type. These experiments should provide an improvement in our ability to predict betaturn sites in globular proteins and should define protein engineering design principles for the hybrid proteins above and other new protein molecules in general. NMR and x-ray crystallography experiments will continue in an effort to define the physical basis by which a cis peptide bond is favored in a type VI beta-turn of staphylococcal nuclease. This system provides an opportunity to observe the influence of amino acid sequence on the equilibrium between two beta-turn types on the surface of a globular protein. A genetic and crystallographic analysis will continue to define sequences consistent with a type I' beta-turn in nuclease, and the physical and structural basis for these sequences preferences.