Proteins, membrane deficiency

DEFICIENCY Vitamin A deficiency results in night blindness and xerophthalmia (dry cornea and conjunctiva, sometimes with ulceration of the cornea). Nonocular changes may also occur dry skin and mucous membranes. Deficiency may result from poor dietary intake, or poor absorption, as from bowel disease, or a defect in bile flow that causes fet malabsorption. Poor protein intake may result in a reduced level of the transport protein that carries vitamin A in the blood stream. 

Fig. 22.2. Lysosomal catabolism of membrane-associated/ hydrophobic proteins. In infantile neuronal ceroid lipofuscinosis (CLNl) palmitoyl protein thioesterase is deficient (22.4.1). Late infantile neuronal lipofuscinosis (CLN2) is due to a defect in tripeptidyl peptidase I (22.4.2). Sub C = subunit C of ATP synthase complex. CLN3 protein = membrane protein of unknown function. It probably contributes to the disposal of organella membranes, it is defective in juvenile neuronal ceroid lipofuscinosis (CLN3, 22.4.3)...

DMD and BMD DMD and BMD are caused by the absence or deficiency of dystrophin a membrane-associated protein, resulting in increased Ca2+ concentration in muscle, loss of Ca2+ homeostasis, and inappropriate calpain activity36... 

Paroxysmal nocturnal hemoglobinuria (MIM 311770) Mutation resulting in deficient attachment of the GPI anchor to certain proteins of the red cell membrane... 

Prothrombin and several other proteins of the blood clotting system (Factors VII, IX and X, and proteins C and S) each contain between four and six y-carboxygluta-mate residues which chelate calcium ions and so permit the binding of the blood clotting proteins to membranes. In vitamin K deficiency or in the presence of warfarin, an abnormal precursor of prothrombin (preprothrombin) containing little or no y-carboxyglutamate, and incapable of chelating calcium, is released into the circulation. 

One cause of hereditary spherocytosis (Figure 52-5) is a deficiency in the amount of spectrin or abnormalities of its structure, so that it no longer tightly binds the other proteins with which it normally interacts. This weakens the membrane and leads to the spherocytic shape. Abnormalities of ankyrin and of bands 3 and 4.1 are involved in other cases. 

On a laboratory scale, the most commonly used E. coli strains are BL21 (protease deficient) and K12 (seems to show enhanced disulfide bond formation) and some optimized derivatives [13] for example, C41 and C43 for membrane proteins expression, Rosetta strains and BL21 CodonPlus strains with overexpressed tRNAs to deal with rare E. coli codons, or JM 83 for proteins secreted into the periplasm. Strains and plasmids are commercially available and were reviewed in several papers [13,26],... 

LBPs are likely to have conventional roles in the energy metabolism and transport of lipids in nematodes for membrane construction, etc. Many parasitic helminths have deficiencies in the synthesis of some lipids and so their lipid acquisition, transport and storage mechanisms clearly need to be specialized and therefore pertinent to the host-parasite relationship (Barrett, 1981). From a practical point of view, lipid transporter proteins may also be important in the delivery of anthelmintic drugs to their target most anthelmintics are hydrophobic and if they do not distribute to their site of action within the parasites by simple diffusion across and along membranes, then the parasite s own carrier proteins may be involved. 

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