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We present an extended structural study of globular complexes made by mixinga positively charge protein (lysozyme) and a negatively charged polyelectrolyte(PSS). We study the influence of all the parameters that may act on thestructure of the complexes (charge densities and concentration of the species,partial hydrophobicity of the polyion chain, ionic strength). The structures ona 15 scale range lying from 10{\AA} to 1000{\AA} are measured by SANS. Whateverthe conditions, the same structure is found, based on the formation of denseglobules of ~ 100{\AA} with a neutral core and a volume fraction of organicspecies (compacity) of ~ 0.3. At higher scale, the globules are arranged infractal aggregates. Zetametry measurements show that globular complexes have atotal positive charge when the charge ratio of species introduced in themixture [-]/[+]intro > 1 and a total 20 negative charge when [-]/[+]intro < 1.This comes from the presence of charged species in slight excess in a layer atthe surface of the globules. The globule finite size is determined by the Debyelength k-1 whatever the way the physicochemical parameters are modified in thesystem, as long as chain-protein interactions are of simple electrostaticsnature. The mean number of proteins per primary complex Nlyso_comp growsexponentially on a master curve with k-1. This enables to picture 25 themechanisms of formation of the complexes. There is an initial stage offormation where the growth of the complexes is only driven by attractionsbetween opposite species associated with counterion release. During the growthof the complexes, the globules progressively repell themselves by electrostaticrepulsion because their charge increases. When this repulsion becomes dominentin the system, globules stop growing and behave like charged colloids: theyaggregate 30 with a RLCA process, which leads to the formation of fractalaggregates of dimension Df 2.1.

Finite size and inner structure controlled by electrostatic screening in globular complexes of proteins and polyelectrolytes