Download Gal

SHINGOLIPIDS/
SHINGOPHOSPHOLIPIDS
METABOLISM
Role of sphingolipids
• Abundant component of myelin sheath (25%
in humans)
• These lipids are in a continuous state of
turnover, defects in this metabolism leads to
various diseases
SPHINGOLIPIDS AT CELL SURFACES ARE SITES OF
BIOLOGICAL RECOGNITION
1.
In humans at least 60 different sphingolipids have
been identified.
2.
Very prominent in neuronal plasma membranes.
3.
Carbohydrate moieties of sphingolipids define the
human blood groups.
4.
The kinds and amounts of gangliosides vary
dramatically during development.
Sphingolipids
• Sphingomyelin contains
sphingosine with a longchain fatty acid attached
in amide linkage ( =
ceramide)
• Ceramide plus a
phosphocholine group
constitutes a
sphingomyelin
• Ceramide is also the core
component of
glycosphingolipids
.
• The backbone of
sphingomyelin is the
amino alcohol sphingosine,
rather than glycerol (Figure
17.4). A long-chain fatty
acid is attached to the
amino group of
sphingosine through an
amide linkage, producing a
ceramide .The alcohol
group at carbon 1 of
sphingosine is esterified to
phosphorylcholine,
producing
SPHINGOMYELIN
SIMILARITIES BETWEEN PHOSPHATIDYL CHOLINE
(A GLYCEROPHOSPHOLID) AND SPHINGOMYELIN (A SPHINGOLIPID)
choline
choline
Prominent in myelin
sheath that surrounds
and insulates neurons
SPHINGOMYELIN
• Sphingomyelin is present in plasma membranes
and in lipoproteins
• It is very abundant in myelin
• Sphingomyelin is abundant in specialized plasma
membrane microdomains called LIPID RAFTS
LIPID RAFTS
• Lipid rafts are specialized microdomains in the
plasma membrane that are rich in sphingomyelin
and cholesterol
• Lipid rafts appear to function in signaling
SPHINGOLIPIDS
SPHINGOSINE:
a long-chain,
unsaturated amino
alcohol, a major
constituent of
sphingolipids, including
sphingomyelins.
The 3-carbon
backbone is
analogous to the
3-carbons of
glycerol.
At C3 there is the
long chain amino
alcohol
sphingosine.
SPHINGOLIPIDS
At C2 there is a fatty
acid which is usually
saturated or
monounsaturated,
and can be either
16,18, 22, or 24
carbons long.
SPHINGOLIPIDS
Ceramide is the
parent compound.
Other polar head
groups can be
attached at position
X.
SPHINGOLIPIDS
Glycosphingolipids are a
sub-group of
sphingolipids that
contain sachharide
headgroups
Glucosyl-ceramide / Glucocerebroside
Glu
Ceramide
Gal
Glu
Ceramide
Gal
Glu
Ceramide
Monohexoside
Dihexoside
Trihexoside
Gal
Biosynthesis of membrane lipids and
steroids 1
15
Galactosyl – ceramide / Galactocerebroside
Monohexoside
Dihexozid
Gal
Biosynthesis of membrane lipids and
steroids 1
Gal
Ceramid
Gal
Ceramid
16
ABO blood group system
Glu
Gal
GalNAc
Gal
„O” (H) antigen
Fuc
Glu
Gal
GalNAc
Gal
GalNAc
„A” antigen
Fuc
Glu
Gal
GalNAc
Gal
Gal
„B” antigen
Fuc
Biosynthesis of membrane lipids and
steroids 1
17
Gangliosides
Gal
GM3
Glu
Ceramide
NANA
GM2
GalNAc
Gal
Glu
Ceramide
Glu
Ceramide
NANA
GM1
GalNAc
Gal
Gal
Cholera toxin
NANA
Biosynthesis of membrane lipids and
steroids 1
18