Investigating the inner structure of irregular $ \beta$ -lactoglobulin spherulites

Abstract

When beta-lactoglobulin in low p H aqueous solutions is exposed to high temperature for extended time, spherulites composed of amyloid fibrils of the beta-lactoglobulin protein form. Many of these spherulites have fibrils that radiate out from a centre and, under crossed polarisers, exhibit a symmetric Maltese Cross structure. However, a significant fraction (50 of the 101 observed spherulites) of beta-lactoglobulin spherulites formed under these conditions demonstrate various forms of irregularity in apparent structure. The irregularities of spherulites structures were qualitatively investigated by comparing optical microscopy images observed under crossed polarisers to computationally produced images of various internal structures. In this way, inner spherulite structures are inferred from microscopy images. Modelled structures that were found to produce computed images similar to some of the experimentally viewed images include fibrils curving as they radiate from a single nucleation point; multiple spherulites nucleating in close proximity to one another; and fibrils curving in opposite directions above and below a single nucleation point.

Tuning the aqueous self-assembly process of insulin by a hydrophobic additive

“…The result for the insulin-only reaction is in agreement with a large number of studies on insulin spherulite formation. [18][19][20][21][22][23] We have earlier reported the preparation of amyloid brils incorporating 6T. In this case we found it benecial to agitate the solutions by magnetic stirring in the initial stages of the aggregation process.…”

“…[13][14][15][16][17] Moreover there is oen concomitant formation of spherical objects, known as spherulites, made up of an amorphous core surrounded by radially oriented amyloid bril-like materials. [18][19][20][21][22][23][24][25][26][27][28][29][30][31] The formation of spherulites is thus a process competing with bril formation. In fact, under many reaction conditions employed for amyloid formation, sperulites rather than brils constitute the main product.…”

Spherulites

“…Donald and co-workers have recently made detailed analyses of protein spherulite growth, , as these processes are related to amyloidosis and associated neurodegeneracies (see next section). They have studied β-lactoglobulin − and lysozyme as well as the aforementioned insulin. Synthetic peptides have been studied by this group and others as well. − Hemoglobin S can also form spherulites …”

Structure of Spherulites in Insulin, β-Lactoglobulin, and Amyloid β

“…The overall retardation along the light path is the sum of the individual retardations from every contributing fibril. At the center of the spherulite, the total retardation is zero due to the cancellation of effects in different directions; it reaches a maximum at approximately two-thirds from the center of the spherulite and then decreases to zero at the periphery, as the decrease in the thickness counteracts the birefringence of the fibers. − …”