Quaternary structures solubility

The Fenna-Matthews-Olson (FMO) protein is an unusual, water-soluble chlorophyll protein found only in green sulfur bacteria. [18] It is believed to be located between the chlorosome and the cytoplasmatic membrane and functions as an excitation transfer link between the chlorosome and the reaction center. Each subunit contains 7 BChl a molecules embedded in a primarily /3 sheet structured protein. The protein has a trimeric quaternary structure, with a three-fold axis of symmetry in the center of the complex. [55] The green nonsulfur bacteria do not contain the FMO protein. In these organisms the chlorosome transfers energy directly to the integral membrane core antenna B808-865, and then to the reaction center. 

Proteins may be fibrous or globular. The structure and polarity of the particular amino acid R groups and their sequence affect the solubility properties and tertiary structure of proteins. Quaternary structure refers to the aggregation of similar protein subunits. 

Primary Structure Protein Solubility Protein Synthesis Protein Translation Quaternary Structure Residue... 

Srivastava PK, Sharma VK, Kalonia DS, Grant DF (2004) Polymorphisms in human soluble epoxide hydrolase effects on enzyme activity, enzyme stability, and quaternary structure. Arch Biochem Biophys 427 164-169... 

The diversity in primary, secondary, tertiary, and quaternary structures of proteins means that few generalisations can be made concerning their chemical properties. Some fulfil structural roles, such as the collagens (found in bone) and keratin (found in claws and beaks), and are insoluble in all solvents. Others, such as albumins or globulins of plasma, are very soluble in water. Still others, which form part of membranes of cells, are partly hydrophilic ( water-loving , hence water-soluble) and partly lipophilic ( lipid-loving , hence fat-soluble). 

The high level of a protein complex with ATPase activity in P. occultum at temperatures near the upper growth limit (11% of the soluble protein at the growth optimum of 100 C 73% at 108 C [53]) led to the suggestion that this protein may be essential for growth at the upper temperature limits of life. Unfortunately, no experimental data are yet available giving information about its physiological role. From its quaternary structure it was concluded that this abundant protein may function as a chaperone. 

The dependence of solubility on temperature varies. We will consider here the range of zero to about 50°C at still higher temperature unfolding may occur. For hydrophilic proteins, the solubility may increase with temperature, by up to 4% per K. For more hydrophobic proteins, solubility decreases with increasing temperature, by up to 10% per K. This is in accordance with the strong temperature dependence of hydrophobic bonds in the range considered (Fig. 3.4). Low temperature may also cause dissociation of quaternary structures. 

Highly optimized hydrophobic interactions can be observed across the monomer-monomer interface between residues related by the noncrystallographic twofold axis, e.g., the conserved residues Ile-111 and Val-146. Hydrophobic packing also involves Ala-4 with Leu-106 from the other monomeric unit. Mutations of residues in the interface region can lead to disruption of the quaternary structure, resulting in the formation of stable SOD monomers. Replacement of the human enzyme s two interface residues Phe-50 and Gly-51 with Glu has resulted in a stable, soluble SOD monomer that is almost devoid of cata-l5d ic activity (60). 

---