Effective interactions and phase behavior of protein solutions in the presence of hexamine cobalt(III) chloride

The European Physical Journal. E, Soft Matter · 5 authors, 1 centre

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This laboratory biophysical study investigated the effects of hexamine cobalt(III) chloride (Hac) on protein interactions and phase behavior. The central result was that Hac, due to its large ionic radius and stable structure, did not induce reentrant condensation in the globular proteins BLG, BSA, HSA, or OVA, unlike smaller multivalent cations.

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This preclinical laboratory study used small-angle X-ray scattering (SAXS), static light scattering (SLS), and dynamic light scattering (DLS) to measure the effective interactions and phase behavior of four model globular proteins (BLG, BSA, HSA, OVA) in aqueous solution with the multivalent cation hexamine cobalt(III) chloride (Hac). The investigation focused on whether Hac could induce reentrant condensation (RC), a phenomenon seen with other multivalent cations. The analysis of reduced second virial coefficients and scattering profiles showed that while Hac induced some protein-protein attraction, the attraction was not sufficiently strong to drive the system into the condensed or redissolved phases characteristic of RC. The study attributes this to the large ionic radius of the Hac cation (420 pm) and its kinetically stable octahedral structure, which differ from smaller, more labile cations that induce RC. The work concludes that these structural properties of Hac limit its ability to form strong ionic bridges or activate sufficient attractive patches on globular protein surfaces, in contrast to its known ability to condense DNA/RNA via hydrogen bonding.

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other

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biomedical research

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ORIGINAL PAPER

PMC10698144

Effective interactions and phase behavior of protein solutions in the presence of hexamine cobalt(III) chloride

The European Physical Journal. E, Soft Matter

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ABSTRACT

Abstract It is well established that deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) exhibit a reentrant condensation (RC) phase behavior in the presence of the trivalent hexamine cobalt(III) cations (Hac) which can be important for their packing and folding. A similar behavior can be observed for negatively charged globular proteins in the presence of trivalent metal cations, such as Y 3+ or La 3+ . This phase behavior is mainly driven by charge inversion upon an increasing salt concentration for a fixed protein concentration ( c p ). However, as Hac exhibits structural differences compared to other multivalent metal cations, with six ammonia ligands (NH 3 ) covalently bonded to the central cobalt atom, it is not clear that Hac can induce a similar phase behavior for proteins. In this work, we systematically investigate whether negatively charged globular proteins β-lactoglobulin (BLG), bovine serum albumin (BSA), human serum albumin (HSA) and ovalbumin (OVA) feature Hac-induced RC. Effective protein–protein interactions were investigated by small-angle X-ray scattering. The reduced second virial coefficient (B 2 /B 2 HS ) was obtained as a function of salt concentration. The virial coefficient analysis performed confirms the reentrant interaction (RI) behavior for BLG without actually inducing RC, given the insufficient strengths of the interactions for the latter to occur. In contrast, the strength of attraction for BSA, HSA and OVA are too weak to show RC. Model free analysis of the inverse intensity 1 / I q → 0 also supports this finding. Looking at different q -range by employing static (SLS) and dynamic light scattering experiments, the presence of RI behavior can be confirmed. The results are further discussed in view of metal cation binding sites in nucleic acids (DNA and RNA), where Hac induced RC phase behavior. Graphical abstract Supplementary Information The online version contains supplementary material available at 10.1140/epje/s10189-023-00376-6.

CITATION EXPORT

Maximilian D Senft, Ralph Maier, Anusha Hiremath et al.. Effective interactions and phase behavior of protein solutions in the presence of hexamine cobalt(III) chloride. The European Physical Journal. E, Soft Matter. (2023). https://doi.org/10.1140/epje/s10189-023-00376-6

AUTHORS

5 · 1 CENTRES

Maximilian D Senft, Ralph Maier, Anusha Hiremath, Fajun Zhang, Frank Schreiber

1Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany