Poly(l-arginine) (PARG) and poly(l-glutamic acid) (PLGA) homopolypeptides were custom synthesized by precision N-carboxyanhydride ring-opening polymerization methods with two molar masses, matched for pairs of cationic and anionic polypeptides (degrees of polymerization n = 100 and n = 500). The conformations of the homopolypeptides were probed using circular dichroism (CD) and FTIR spectroscopy which revealed the presence of mainly polyproline II (PPII) conformation. Small-angle X-ray scattering (SAXS) showed concentration-dependent polyelectrolyte peaks and form factor with high q scaling due to the excluded volume behaviour of the wormlike chains. We then examined polyelectrolyte complexation in mixtures of pairs of PARG and PLGA polypeptides with matched molar masses. Precipitation was generally observed and the structures of precipitates, supernatant and resuspended precipitates were investigated using CD, SAXS and cryo-TEM. These revealed that, contrary to prior suggestions in the literature, the precipitates contain mostly polypeptides in a PPII-like conformation, and there is only a minimal β-sheet content (which is enhanced upon drying the sample during preparation for certain measurements). The precipitates have a fractal-like structure as revealed by cryo-TEM and SAXS. Our findings on the structure of polypeptide complex precipitates contribute to the understanding of phase separation of polyelectrolyte complexes and coacervation and may shed light on the formation of inter-cellular bodies of proteins and peptides such as Lewy and other inclusion bodies.

聚（l-精氨酸）（PARG）和聚（l-谷氨酸）（PLGA）均聚肽是通过精密N-羧酸酐开环聚合方法定制合成的，具有两个摩尔质量，匹配阳离子和阴离子多肽对（度数聚合n  = 100 和n  = 500)。使用圆二色性 (CD) 和 FTIR 光谱探测同源多肽的构象，发现主要存在聚脯氨酸 II (PPII) 构象。小角度 X 射线散射 (SAXS) 显示浓度依赖性聚电解质峰和具有高q的形状因子由于蠕虫链的排除体积行为而缩放。然后，我们检查了具有匹配摩尔质量的 PARG 和 PLGA 多肽对混合物中的聚电解质络合。通常观察沉淀，并使用 CD、SAXS 和冷冻 TEM 研究沉淀物、上清液和再悬浮沉淀物的结构。这些表明，与文献中先前的建议相反，沉淀物主要包含 PPII 样构象的多肽，并且只有极少的 β-折叠含量（在某些测量的制备过程中干燥样品后会增强）。如冷冻 TEM 和 SAXS 所示，沉淀物具有分形结构。