Stability-related structural proteins

The structure and function of enzymes is determined by both the amino acid sequence and the surrounding solvent. The overall stability of proteins is characterized by a subtle balance of into- and inter-molecular interactions. The basic principle of the structure (and of the stability) of the proteins is related to the nature of its normal enviromnent for (water) soluble globular proteins this is the minimization of the hydrophobic surface area, whereas the contrary is the case for membrane proteins (Jaenicke, 1991). 

Support for this picture can be found in a study of the two closely related mesophilic proteins barnase and binase. These two extracellular ribonucleases are highly similar in structure, stability, and sequence, differing by only seventeen out of 110 amino acids. Serrano et al. (1993) introduced each mutation present in binase into barnase and measured... 

However, another study was an example of nature appreciation—the structure of thiamine was varied to learn what was special about the particular thiazolium derivative that was natural thiamine (11). As a chemical catalyst—ignoring the question of what effect changes would have on the ability of the coenzyme to bind to the proteins that have evolved to use it—thiamine proved to be the optimal relative to other related structures because of a balance of catalytic ability and chemical stability. The anion 4 derived from an imidazolium ring instead of a thiazolium ring was a weaker catalyst but was more stable in water (10). [The imidazolium aiuon and its dihydro derivative have proven to be very useful metal ion ligands, including... 

The detection of one zinc atom per zinc finger sequence (or to a related zinc-binding sequence) docs not necessarily mean that the protein actually requires zinc for activity. The researcher needs to determine that the zinc actually /unctions to support activity to support a regulatoiy property, or to stabilize the structure of the protein before claiming that the pn>lein is a zinc metalloprotein. The simplest method used to assess if a protein requires zinc for activity is to men sure the activity in the presence and absence of a chelator, such as ethyle-nediaminctetrancetic acid (EDTA). fiowever, one should be cautioned that the... 

Increasing levels of emulsification significantly depleted protein from the fat globule in the mix. The adsorbed protein content in the mix (mg m of fat surface area) correlated with major characteristic analyses describing the fat structure in ice cream (fat agglomerate size, fat agglomeration index, solvent extractable fat Fig. 6). Thus, the measurement of protein load in the mix can be used to predict ice-cream-fat stability and related structure. Structural analyses indicated enhanced interaction between fat and air as protein adsorption decreased. It was also observed that the fat content in the dripped portion collected from a meltdown test correlated well with other indices of fat destabilization. 

In the case of the major cytoplasmic protein of leaves, ribulose 1,5-biphosphate carboxylase (RUBISCO), the surface rheological properties and foam stability were maximum at pH 5.5, close to the isoelectric point (pH 4.8) and all parameters measured were greater than any other protein studied (2 ). This may be related to the large molecular size of RUBISCO, i.e. 560 000 daltons, and its disulfide stabilized globular structure. 

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