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Receptor and Signaling > Calcium Signaling II > Flashcards

Calcium Signaling II Flashcards

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1
Q

what are the two Ca binding domains

A

C2 domain and EF-hand domain

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2
Q

what is the structure of EF-hand domain

A

“helix-loop-helix” protein motif, with the loop specialized to
bind a metal ion

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3
Q

what part of the EF hand domain bind to Ca ion?

A

helix-loop

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4
Q

what are the two classes of EF-hand domain

A

Ca buffers and Ca sensors

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5
Q

__________ types of EF-hand domain does not alter protein and _____________ change protein conformation

A

Ca buffers

Ca Sensors

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6
Q

Give 3 examples of Ca buffer and 5 examples of Ca sensors

A

Ca2+ buffers
• Calbindin D-28k (6 EF-hands)
• Parvalbumin (3 EF-hands)
• Calretinin (6 EF-hands)

 Ca2+ sensors 
• Calmodulin (4 EF-hands)
• Troponin C (4 EF-hands)
• Calcineurin B (4 EF-hands)
• Calpain (5 ER-hands)
• S100 proteins (a large family)
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7
Q

where does Ca interact in the EF-hand domain ?

A

ca interacts with with O2 atom mainly of glutamate and aspartate side-chain
groups) in the loop

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8
Q

what does s100% mean

A

Soluble in 100% ammonium sulfate

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9
Q

what is calmodulin

A

A ubiquitous Ca2+-binding protein

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10
Q

what and how many Ca does one calmodulin bind to be activated

A

Each molecule of CaM cooperatively binds 4 Ca2+(4 EF-hand domains); all 4
sites must be occupied by Ca2+ for CaM function

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11
Q

does CaM have enzymatic activity?

A

CaM has no enzymatic activity, even when bound to 4 Ca2+ ions!!!

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12
Q

how does CaM function?

A

interaction with Ca2+/CaM à change
conformation of target protein (often
by relieving autoinhibition) à altered
target protein function

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13
Q

What is CaM-Kinase

A

A family of serine/threonine kinases that mediate many of the effects of Ca2+/CaM

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14
Q

what are the types of CaM-kinases

A
  1. Substrate-restricted: Responsible for phosphorylation of a specific substrate
  2. Multifunctional
    Broad substrate specificity
    CaM-kinase II (CaMKII) is the most prominent example
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15
Q

what are CaM-kinase II substrates

A

tyrosine hydroxylase
ion channels
CaM-kinase II

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16
Q

what factors increase Ca

A

Receptor complexes
that generate IP3
Membrane Ca2+
channels

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17
Q

what factors decrease Ca

A

Ca2+ pumps and
exchangers
Ca2+ buffers

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18
Q

what are membrane Ca channels

A

§ Located in the plasma membrane and in membranes delimiting organelles

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19
Q

Channel opening allows _____________movement of Ca2+ down______________

A

passive

electrochemical gradient.

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20
Q

what are the membrane potentials for plasma membrane and mitochondrial membrane

A

Plasma membrane is inside-negative (-70 mV)

Mitochondrial membrane is matrix-negative (-150 mV)

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21
Q

what is the Ca concentration for resting state for extracellular fluid, cytosol and ER?

A

EF: 2mM
cytosol: 100nM
ER: 300-800uM

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22
Q

what is the Ca concentration for stimulated state for extracellular fluid, cytosol and ER?

A

EF: 2mM
cytosol: 1000nM
ER: 100uM

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23
Q

How does Plasma membrane involved in Ca channels

A

Provide an avenue for sustained Ca2+ entry into the cell, allowing prolonged elevations
of Ca2+

Multiple types of Ca2+ channels

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24
Q

what are types of Ca channels

A

ligand-gated
voltage-gated
store-operated

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25
Voltage gated ion channel has _______ pore forming ___________ subunit
4 | pore-forming (a1) subunit
26
how many subunits does Voltage gated Ca Channel
4 accessory subunits
27
discuss structure of Voltage gated Ca channel a1 subunit
4 pore-forming domains (I-IV), each with 6 transmembrane | segments (S1-S6) connected by intracellular or extracellular loops
28
Nifedipine
specifically blocks Cav1 (L-type) important antihypertensive agent
29
EGTA
avidly binds extracellular Ca2+ (calcium chelator) | blocks all responses dependent upon Ca2+ influx regardless of the type of Ca2+ channel
30
a1 subunit pore loop confer to ______
Ca selectivity
31
a1 subunit Regulatory domain confer to _____________
* EF-hand (Ca2+) * Ca2+/CaM * PKC
32
How does ER/SR membrane involved in Ca channels
Allows rapid Ca2+ mobilization from intracellular “stores”
33
ER/SR Ca channels are ________________ gated | what are the two types
ligand two types IP3 receptor Ryanodine receptor
34
what are IP3 receptors
A ubiquitous ligand-gated ion channel in the ER or SR membrane homo- or hetero-tetramer
35
IP3 regulatory domain has
Ca binding ATP binding phosphorylation site
36
how many domains does IP3 has
Regulatory domain IP3 binding domain Channel domain
37
Ca2+ release via IP3Rs is a primary signal to activate processes in ______________ cells. give examples
non-excitable cells ``` • Fertilization (oocytes) • Proliferation (lymphocytes) • Metabolism (hepatocytes) • Secretion (salivary gland; pancreas) ```
38
IP3R activation usually triggers brief ______________
transients of Ca2+ release
39
_________ responses generally involve repeated spikes/oscillations.
longer duration
40
Oscillation frequency characteristically depends on the level of _____________
stimulus intensity.
41
what are the three IP3R isoforms
IP3R1, IP3R2, IP3R3
42
what is the point of the three IP3R isoforms
similar primary structures but different physiological properties allows cells to create IP3-dependent [Ca2+]i signals with distinct spatial and temporal characteristics to control many cellular functions
43
_____________ in the cytosol are required for channel opening (primary regulators)
IP3 and Ca2+
44
Channel activation
↑[IP3]i à 4 IP3 molecules bind to the IP3R tetramer à conformation change sensitizes Ca2+ binding site à Ca2+ binds à conformation change opens the pore à Ca2+ release into cytosol.
45
what are the secondary regulation of IP3R activity
Factors that tend to ↑IP3R activity cytoplasmic nucleotides (ATP) PKA-mediated phosphorylation reactive oxygen species tumor suppressors Factors that tend to ↓IP3R activity PKG-mediated phosphorylation Protooncogenes Very high [Ca2+]i (> 300 nM), likely through Ca/CaM
46
Xestospongin C
membrane-permeable | sterically blocks Ca2+ pore
47
Heparin
membrane impermeable | competes for IP3 binding
48
Ryanodine receptor (RyR)
A ligand-gated ion channel in the ER/SR | membrane, structurally related to the IP3R
49
The functional channel of Ryanodine receptor (RyR) | is a
homotetramer
50
what are the isoforms Ryanodine receptor (RyR)
3 isoforms: RyR1 (skeletal muscle) RyR2 (cardiac muscle) RyR3 (more ubiquitous)
51
what is calsequestrin
a Ca2+-binding | protein
52
________________ draw calsequestrin into a complex with the RyR
Junctin & triadin
53
___________ maintains proper spacing between SR | and plasma membran
Junctophilin
54
Ryanodine
a plant alkaloid | μM concentrations inhibit channel opening
55
Caffeine
mM concentrations activate the RyR
56
``` Ca2+ release via RyRs and influx via VGCCs are primary signals for activating processes in ________________ ``` give example
* Contraction (muscle) * Insulin secretion (b cells) * Excitability (neurons)
57
______________ is the primary activator of RyRs
Cytosolic Ca2+
58
Source of the an increase in Ca is
Ca2+ channels in the plasma membrane or in the ER/SR, even nearby RyRs (resulting in a wave of RyR activation and Ca2+ release from the ER/SR)
59
In excitable cells, plasma membrane depolarization sensed by _______________ opening of RyRs via _____________ or _____________ mechanisms
voltage-gated Ca2+ channels (VGCCs) direct or indirect mechanisms
60
direct mechanism of RyR is ____________ muscle and indirect mechanism is _______ muscle
skeletal cardiac
61
direct mechanism of RyR is through ________________ of plasma membrane VGCCs with RyRs in SR membrane
Physical coupling
62
Indirect mechanism of RyR is through _____________ positions RyRs in SR membrane close to plasma membrane VGCCs
Junctophilin
63
what is the role of Ca2+ pumps and exchangers
to remove Ca2+ from the cytosol Keep [Ca2+]i low under resting conditions Restore low [Ca2+]i after a Ca2+-dependent stimulus Either extrude Ca2+ from the cell or sequester it into organelles
64
what are the two types of Ca pumps
Plasma membrane Ca2+-ATPase (PMCA) Sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA)
65
what are the two types of Ca exchange
Na+/Ca2+ exchanger (NCX) Na+/Ca2+/K+ exchanger (NCKX)
66
PMCA Hydrolyzes __________ molecule to extrude _____________ Ca2+ from the cell against its electrochemical gradient
1 ATP | 1 Ca2
67
PMCA has ____________ Ca affinity but _______ capacity
High affinity low capacity
68
_____________ Provides the major route of Ca2+ extrusion at resting [Ca2+]i (~100 nM)
PMCA
69
PMCA is Regulated primarily by________
Ca2+/CaM
70
What is the similarity between PMCA and SERCA
A primary active transporter High affinity & low capacity
71
SERCA Hydrolyzes ___________ molecule to pump _________ into the SR/ER against its concentration gradient
1 ATP 2Ca2+
72
Thapsigargin
specific & potent | forms a dead-end complex
73
Cyclopiazonic acid
competitive at the ATP | binding site
74
how do we regulate SERCA
↑ [Ca2+]i à ↑ SERCA activity Protein kinase A-dependent phosphorylation of phospholamban (PLB) à ↑ SERCA activity Inhibited by high [Ca2+] in the ER or SR lumen
75
Ca2+-binding proteins in the lumen keep [Ca2+]ER/SR in the ________range
uM
76
______________(in ER) and ___________(in SR) are high capacity, low affinity Ca2+ buffers that can bind up to 50 Ca2+ per molecule
Calreticulin (in ER) and Calsequestrin (in SR)
77
_______________ is a secondary active transport
NCX
78
NCX relies on the inwardly-directed __________ to drive uphill extrusion of _____________ from the cell.
3 Na+ electrochemical gradient t | 2 Ca2+ from the cell
79
why is NCX important when cytosolic Ca rise
Low Ca2+ affinity, but very high capacity
80
NCX processes ______ cycles/sec Ca during influx
5000 cells/sec
81
how is NCX regulated?
by Ca | [Ca2+]ià ↑ NCX activity
82
NCX has ________ Ca binding domains?
2 Ca
83
Refilling the Ca2+ store is called _______________
Capacitative Ca2+ influx
84
↓ [Ca2+]SR/ER à activation of “X ________________ in the plasma membrane à Ca2+ influx into a sub-plasmalemmal space
“Store-Operated Channels” (SOCs)
85
EGTA
Ca2+ chelators that bind free Ca2+, thus preventing Ca2+- | dependent effects
86
A23187, others
Ca2+ ionophores that let Ca2+ flow freely across cell | membranes
87
Thapsigargin, Cyclopiazonic Acid
SERCA inhibitors that prevent Ca2+ reuptake into ER/SR
88
Xestospongin
current best IP3R blocker
89
Nifedipine (a dihydropyridine), others
blocks Ca2+ influx through | voltage-gated Ca2+ channels (DHPRs)
90
Ryanodine (µM concentrations)
blocks RyRs
91
Caffeine (mM concentrations)
activates RyR
92
PMA (phorbol ester)
activates conventional & novel PKC isoforms
93
Calphostin C
inhibits PKC

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