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Sensitivity of cholecystokinin receptors to membrane cholesterol content.

Desai AJ, Miller LJ - Front Endocrinol (Lausanne) (2012)

Bottom Line: The effects of cholesterol can be mediated directly by specific molecular interactions with the receptor and/or indirectly by altering the physical properties of the membrane.This review focuses on the importance and differential effects of membrane cholesterol on the activity of cholecystokinin (CCK) receptors.This is believed to have substantial potential importance for the development of drugs targeting the CCK receptor.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic Scottsdale, AZ, USA.

ABSTRACT
Cholesterol represents a structurally and functionally important component of the eukaryotic cell membrane, where it increases lipid order, affects permeability, and influences the lateral mobility and conformation of membrane proteins. Several G protein-coupled receptors have been shown to be affected by the cholesterol content of the membrane, with functional impact on their ligand binding and signal transduction characteristics. The effects of cholesterol can be mediated directly by specific molecular interactions with the receptor and/or indirectly by altering the physical properties of the membrane. This review focuses on the importance and differential effects of membrane cholesterol on the activity of cholecystokinin (CCK) receptors. The type 1 CCK receptor is quite sensitive to its cholesterol environment, while the type 2 CCK receptor is not. The possible structural basis for this differential impact is explored and the implications of pathological states, such as metabolic syndrome, in which membrane cholesterol may be increased and CCK1R function may be abnormal are discussed. This is believed to have substantial potential importance for the development of drugs targeting the CCK receptor.

No MeSH data available.


Related in: MedlinePlus

Schematic representation of the alignment of structural segments of the CCK1R and CCK2R. The CCM (red) and the CRAC (violet) are highlighted within the transmembrane segments (rectangles) and intracellular loops (black line) of the CCK1R (top, blue) and CCK2R (bottom, gray).
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Figure 1: Schematic representation of the alignment of structural segments of the CCK1R and CCK2R. The CCM (red) and the CRAC (violet) are highlighted within the transmembrane segments (rectangles) and intracellular loops (black line) of the CCK1R (top, blue) and CCK2R (bottom, gray).

Mentions: In contrast, the other subtype of CCK receptor, the CCK2R, is not sensitive to alterations in membrane cholesterol (Potter et al., 2012). As noted earlier, these receptors are highly homologous and, in fact, share all of the predicted cholesterol binding motifs (Figure 1). The key structural determinant for cholesterol sensitivity appears to reside in the third exon of the CCK1R which encodes most of the transmembrane segment three and four, including one CRAC motif and one CCM motif (Potter et al., 2012). It should be noted that the CCK1R and CCK2R do not contain the entire four-component strict-CCM, but a less restrictive CCM motif that is shared by 44% of human class A GPCRs (Hanson et al., 2008). This is due to the absence of an aromatic residue at 2.41. The relevant contributors to this effect were further studied with site-directed mutants (Potter et al., 2012). This suggested that three residues, Y140 (Y3.51), which is a part of the CRAC motif (Li and Papadopoulos, 1998) in transmembrane segment three, W166 (W4.50), which is a part of the CCM (Hanson et al., 2008) in transmembrane segment four and Y237 (Y5.66), which is part of the CRAC motif in transmembrane segment five, are important for the cholesterol sensitivity of the CCK1R. It is noteworthy that mutation of each of the three residues has negative effects on either CCK binding or CCK-induced signaling. Mutation of Y140 to alanine leads to reduced signaling but increased CCK binding affinity and is insensitive to reduction in membrane cholesterol levels. On the other hand, mutation of W166 to alanine leads to decreased CCK binding and signaling ability of the CCK1R, with a further reduction in signaling upon depleting membrane cholesterol. The Y237A mutant displays no change in signaling, but reduced CCK binding affinity, whereas cholesterol reduction results in the reduction of both parameters. Corresponding single residue mutations (Y153A, W179A, Y246A) within the CRAC and the CCM motifs of the CCK2R did not modify receptor function.


Sensitivity of cholecystokinin receptors to membrane cholesterol content.

Desai AJ, Miller LJ - Front Endocrinol (Lausanne) (2012)

Schematic representation of the alignment of structural segments of the CCK1R and CCK2R. The CCM (red) and the CRAC (violet) are highlighted within the transmembrane segments (rectangles) and intracellular loops (black line) of the CCK1R (top, blue) and CCK2R (bottom, gray).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3475150&req=5

Figure 1: Schematic representation of the alignment of structural segments of the CCK1R and CCK2R. The CCM (red) and the CRAC (violet) are highlighted within the transmembrane segments (rectangles) and intracellular loops (black line) of the CCK1R (top, blue) and CCK2R (bottom, gray).
Mentions: In contrast, the other subtype of CCK receptor, the CCK2R, is not sensitive to alterations in membrane cholesterol (Potter et al., 2012). As noted earlier, these receptors are highly homologous and, in fact, share all of the predicted cholesterol binding motifs (Figure 1). The key structural determinant for cholesterol sensitivity appears to reside in the third exon of the CCK1R which encodes most of the transmembrane segment three and four, including one CRAC motif and one CCM motif (Potter et al., 2012). It should be noted that the CCK1R and CCK2R do not contain the entire four-component strict-CCM, but a less restrictive CCM motif that is shared by 44% of human class A GPCRs (Hanson et al., 2008). This is due to the absence of an aromatic residue at 2.41. The relevant contributors to this effect were further studied with site-directed mutants (Potter et al., 2012). This suggested that three residues, Y140 (Y3.51), which is a part of the CRAC motif (Li and Papadopoulos, 1998) in transmembrane segment three, W166 (W4.50), which is a part of the CCM (Hanson et al., 2008) in transmembrane segment four and Y237 (Y5.66), which is part of the CRAC motif in transmembrane segment five, are important for the cholesterol sensitivity of the CCK1R. It is noteworthy that mutation of each of the three residues has negative effects on either CCK binding or CCK-induced signaling. Mutation of Y140 to alanine leads to reduced signaling but increased CCK binding affinity and is insensitive to reduction in membrane cholesterol levels. On the other hand, mutation of W166 to alanine leads to decreased CCK binding and signaling ability of the CCK1R, with a further reduction in signaling upon depleting membrane cholesterol. The Y237A mutant displays no change in signaling, but reduced CCK binding affinity, whereas cholesterol reduction results in the reduction of both parameters. Corresponding single residue mutations (Y153A, W179A, Y246A) within the CRAC and the CCM motifs of the CCK2R did not modify receptor function.

Bottom Line: The effects of cholesterol can be mediated directly by specific molecular interactions with the receptor and/or indirectly by altering the physical properties of the membrane.This review focuses on the importance and differential effects of membrane cholesterol on the activity of cholecystokinin (CCK) receptors.This is believed to have substantial potential importance for the development of drugs targeting the CCK receptor.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic Scottsdale, AZ, USA.

ABSTRACT
Cholesterol represents a structurally and functionally important component of the eukaryotic cell membrane, where it increases lipid order, affects permeability, and influences the lateral mobility and conformation of membrane proteins. Several G protein-coupled receptors have been shown to be affected by the cholesterol content of the membrane, with functional impact on their ligand binding and signal transduction characteristics. The effects of cholesterol can be mediated directly by specific molecular interactions with the receptor and/or indirectly by altering the physical properties of the membrane. This review focuses on the importance and differential effects of membrane cholesterol on the activity of cholecystokinin (CCK) receptors. The type 1 CCK receptor is quite sensitive to its cholesterol environment, while the type 2 CCK receptor is not. The possible structural basis for this differential impact is explored and the implications of pathological states, such as metabolic syndrome, in which membrane cholesterol may be increased and CCK1R function may be abnormal are discussed. This is believed to have substantial potential importance for the development of drugs targeting the CCK receptor.

No MeSH data available.


Related in: MedlinePlus