Phosphorylation Of Calmodulin-dependent Protein Kinase Research Articles

Icariin inhibits hypertrophy by regulation of GPER1 and CaMKII/HDAC4/MEF2C signaling crosstalk in ovariectomized mice

Icariin (ICA), a flavonoid phytoestrogen, was isolated from traditional Chinese medicine Yin Yang Huo (Epimedium brevicornu Maxim.). Previous studies reporting the cardioprotective effects of ICA are available; however, little is known about the impact of ICA on cardioprotection under conditions of reduced estrogen levels. This study aimed to provide detailed information regarding the antihypertrophic effects of ICA in ovariectomized female mice. Female mice were subjected to ovariectomy (OVX) and transverse aortic constriction and then orally treated with ICA at doses of 30, 60 or 120 mg/kg/day for 4 weeks. Morphological assessments, echocardiographic parameters, histological analyses, and immunofluorescence were performed to evaluate cardiac hypertrophy. Cardiomyocytes from mice or rats were stimulated using phenylephrine, and cell surface and hypertrophy markers were tested using immunofluorescence and qPCR. Western blotting, qPCR, and luciferase reporter gene assays were used to assess the expression of proteins and mRNA and further investigate the proteins related to the G-protein coupled estrogen receptor (GPER1) and CaMKII/HDAC4/MEF2C signaling pathways in vivo and in vitro. ICA blocks cardiac hypertrophy induced by pressure overload in OVX mice. Additionally, we demonstrated that ICA activated GPER1 and inhibited the nuclear export or promoted the nuclear import of histone deacetylase 4 (HDAC4) through regulation of phosphorylation of calmodulin-dependent protein kinase II (CaMKII) and further improved the repression of myocyte enhancer factor-2C (MEF2C). ICA ameliorated cardiac hypertrophy in OVX mice by activating GPER1 and inhibiting the CaMKII/HDAC4/MEF2 signaling pathway.

Commensal microbe-derived SCFA alleviates atrial fibrillation via GPR43/NLRP3 signaling.

Rationale: Dysbiotic gut microbiota (GM) and NLRP3 inflammasome are proarrhythmic factors in atrial fibrillation (AF). Herein, whether short-chain fatty acid (SCFA) produced from GM fermentation of dietary fiber serving as invisible mediators is yet unclear. Thus, the current study aimed to determine whether SCFA alleviated from NLRP3 signaling-mediated atrial remodeling protects AF development.Methods: First, a cross-sectional study based on the GC-MS metabolomics was performed to explore the association between fecal SCFA levels and AF traits in a cohort consisted of 48 individuals. Then, a well-established mice model fed diet deficient or enriched in dietary fiber was established to elucidate the pathophysiological role of SCFA involved in AF susceptibility, atrial remodeling, and G-protein-coupled receptor 43 (GPR43)/NLRP3 signaling. Finally, the effects of SCFA were verified on HL-1 cells.Results: Fecal SCFA levels were remarkably reduced in AF patients with a declining trend from paroxysmal to persistent AF. Prolonged P wave duration based on surface ECG and increased left atrial diameter gained from echocardiography was identified in low-fiber diet mice but lost in SCFA-supplemented group. Lack of dietary fiber enhanced susceptibility to AF under burst pacing, whereas SCFA might exert a protective effect. The supplementation of SCFA prevented dietary fiber deficiency-upregulated phosphorylation of calmodulin-dependent protein kinase II and ryanodine receptor 2, the disarray fibrosis, collagen expression, and NLRP3 inflammasome activation in atrial tissue. Finally, the AF protective roles of SCFA were identified through GPR43 mediated deactivation of NLRP3 by GPR43 knockdown in HL-1 cells.Conclusions: SCFA derived from dietary fiber fermentation by gut commensals alleviates AF development via GPR43/NLRP3 signaling.

Protective effect of microorganism biotransformation-produced resveratrol on the high fat diet-induced hyperlipidemia, hepatic steatosis and synaptic impairment in hamsters.

Background: Resveratrol, a natural antioxidant polyphenol, has the functions of anti-inflammation, anti-cancer, liver protection and cardioprotection. Microorganism biotransformation-produced resveratrol (MBR) product shows higher purity than the natural source of resveratrol and costs less than the chemically synthesized resveratrol. The aim of the present study was to investigate the protective effects of MBR in hamsters treated with a high-fat diet (HFD).Methods: MBR was obtained by the fermentative process of piceid. Hamsters were randomly divided into four groups: HFD plus oral administration of MBR 0 (C), 5 (L), 20 (M) or 50 mg/kg (H), respectively. After six-week of treatment, hamsters were sacrificed, and tissues were collected for further analysis.Results: MBR at these three dosages did not influence the appetite or growth of the hamsters. Liver enzymes, blood glucose, total cholesterol, triglyceride, and liver weight were significantly reduced in the MBR groups than in the control group. Additionally, high-density lipoprotein-cholesterol (HDL-C) was also elevated in all MBR groups. On the other hand, serum low-density lipoprotein-cholesterol (LDL-C) was decreased in the MBR groups. Triglyceride (TG) in liver tissue and fatty liver level were lower in group H. Memory-associated proteins, phosphorylation of calmodulin-dependent protein kinase II (p-CaMK II) and synaptophysin (SYP), were increased in the brains of MBR groups.Conclusion: The high yield- and short procedure-produced MBR has the potential to protect animals fed with HFD from hyperlipidemia, hepatic steatosis, hyperglycemia, and synaptic impairment, which might be beneficial for patients with these types of diseases.

Standardized Bacopa monnieri Extract Ameliorates Learning and Memory Impairments through Synaptic Protein, Neurogranin, Pro-and Mature BDNF Signaling, and HPA Axis in Prenatally Stressed Rat Offspring

Prenatal stress (PNS) influences offspring neurodevelopment, inducing anxiety-like behavior and memory deficits. We investigated whether pretreatment of Bacopa monnieri extract (CDRI-08/BME) ameliorates PNS-induced changes in signaling molecules, and changes in the behavior of Wistar rat offspring. Pregnant rats were randomly assigned into control (CON)/prenatal stress (PNS)/PNS and exposed to BME treatment (PNS + BME). Dams were exposed to stress by placing them in a social defeat cage, where they observed social defeat from gestational day (GD)-16–18. Pregnant rats in the PNS + BME group were given BME treatment from GD-10 to their offspring’s postnatal day (PND)-23, and to their offspring from PND-15 to -30. PNS led to anxiety-like behavior; impaired memory; increased the level of corticosterone (CORT), adrenocorticotropic hormone, glucocorticoid receptor, pro-apoptotic Casepase-3, and 5-HT2C receptor; decreased anti-apoptotic Bcl-2, synaptic proteins (synaptophysin, synaptotagmin-1), 5-HT1A, receptor, phosphorylation of calmodulin-dependent protein kinase II/neurogranin, N-methyl-D-aspartate receptors (2A,2B), postsynaptic density protein 95; and conversion of pro and mature brain derived neurotropic factor in their offspring. The antioxidant property of BME possibly inhibiting the PNS-induced changes in observed molecules, anxiety-like behavior, and memory deficits. The observed results suggest that pretreatment of BME could be an effective coping strategy to prevent PNS-induced behavioral impairments in their offspring.

MCLR induces dysregulation of calcium homeostasis and endoplasmic reticulum stress resulting in apoptosis in Sertoli cells

Microcystins-LR (MCLR) is a potent reproductive system toxin. We have previously shown that MCLR induced endoplasmic reticulum (ER) stress and apoptosis in testis. ER is the main calcium storage site in cells, and its calcium homeostasis plays an important role in the regulation of apoptosis. Hence, in the present study, we have investigated the role of calcium (Ca2+) in inducing apoptosis and how it affect the mitochondria and endoplasmic reticulum in TM4 cells. Our study found that MCLR induced an increase in Ca2+ concentration in TM4 cells. Compared to the controls, MCLR induced phosphorylation of calmodulin-dependent protein kinase II (CaMKII) which was involved in MAPKs activation, resulting in the induction of mitochondrial apoptosis pathways. Ca2+ chelator Bapta-AM partially reversed MCLR-induced apoptosis, confirming the possible involvement of calcium homeostasis disruption after MCLR exposure. Meanwhile, MCLR activated unfolded protein response and activated the ER apoptotic pathway by activating caspase-12. In addition, exposure to MCLR causes mitochondrial defects and increased apoptosis by up-regulating caspase 3 and cytosol cytochrome c expression. Collectively, these results demonstrated that MCLR disturbed calcium homeostasis, which caused ER-mitochondria dysfunction, ultimately promoted cell apoptosis in Sertoli cells.

Sesamin Induces Endothelial Nitric Oxide Synthase Activation via Transient Receptor Potential Vanilloid Type 1.

Sesamin, the most abundant lignan in sesame seed oil, has many biological activities. However, the underlying molecular mechanisms behind the regulatory effects of sesamin on endothelial nitric oxide synthase (eNOS) activity and nitric oxide (NO) generation in endothelial cells (ECs) remain unclear. Sesamin induced the intracellular level of NO and eNOS phosphorylation in ECs in a concentration- and time-dependent manner. Additionally, sesamin induced levels of intracellular calcium, leading to the phosphorylation of calmodulin-dependent protein kinase II (CaMKII) at Thr286, calcium/calmodulin-dependent protein kinase kinase beta (CaMKKβ) at Ser511, protein kinase A (PKA) at Thr197, Akt at Ser473, and AMP-activated protein kinase (AMPK) at Thr172. In particular, blocking of the transient receptor potential vanilloid type 1 (TRPV1) channel by capsazepine (TRPV1 antagonist), as well as TRPV1 knockdown via TRPV1 silencing RNA, abrogated sesamin-induced PKA, Akt, AMPK, CaMKII, CaMKKβ, and eNOS phosphorylation and NO level in ECs. Furthermore, sesamin inhibited TNF-α-induced NF-κB translocation, intercellular adhesion molecule-1 expression, and monocyte adhesion. Sesamin triggered eNOS activity and NO production via activation of TRPV1-calcium signaling, which involved the phosphorylation of PKA, CaMKII, CaMKKβ, Akt, and AMPK. Sesamin may be useful for treating or preventing the endothelial dysfunction correlated with cardiovascular diseases.

Effects of Coffee Components on Muscle Glycogen Recovery: A Systematic Review

Coffee is one of the most consumed beverages in the world, and it can improve insulin sensitivity, stimulating glucose uptake in skeletal muscle when adequate carbohydrate intake is observed. The aim of this review is to analyze the effects of coffee and coffee components on muscle glycogen metabolism. A literature search was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analysis, and seven studies were included, that explored the effects of coffee components on various substances and signaling proteins. In one of the studies with humans, caffeine was shown to increase glucose levels, Ca2+/calmodulin-dependent protein kinase phosphorylation, glycogen resynthesis rates, and glycogen accumulation after exercise. After intravenous injection of caffeine in rats, caffeine increased adenosine monophosphate-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) phosphorylation, and glucose transport. In in vitro studies, caffeine raised AMPK and ACC phosphorylation, increasing glucose transport activity and reducing energy status in rat muscle cells. Cafestol and caffeic acid increased insulin secretion in rat beta cells and glucose uptake into human muscle cells. Caffeic acid also increased AMPK and ACC phosphorylation, reducing the energy status and increasing glucose uptake in rat muscle cells. Chlorogenic acid did not show any positive or negative effect. The findings from this review must be taken with caution due to the limited number of studies on the subject. In conclusion, various coffee components had a neutral or positive role in the metabolism of glucose and muscle glycogen, whereas no detrimental effect was described. Coffee beverages should be tested as an option for athletes' glycogen recovery.

Mechanisms Underlying a Decrease in KCl-Induced Contraction after Long-Term Serum-Free Organ Culture of Rat Isolated Mesenteric Artery

ABSTRACTOrgan culture of blood vessel is a better technique to investigate the long-term effects of drugs. However, some functional changes may occur from freshly isolated vessel (Fresh). Mammalian/mechanistic target of rapamycin (mTOR) regulates smooth muscle differentiation and Ca2+ mobilization. We thus investigated mechanisms of alteration in smooth muscle contractility after serum-free organ culture focusing on mTOR. Rat isolated mesenteric arteries were cultured for 5 days without (0% serum) or with rapamycin. In 0% serum, absolute contraction by KCl significantly decreased from Fresh, which was significantly rescued by rapamycin. In 0% serum, mTOR expression significantly increased from Fresh, which was significantly rescued by rapamycin. In 0% serum, expression of myocardin, a key regulator of smooth muscle differentiation markers, significantly decreased from Fresh, which was significantly rescued by rapamycin. However, the decrease in expression of contractile proteins, including SM22α and calponin, was not changed by rapamycin. Basal phosphorylation of calmodulin-dependent protein kinase II significantly increased in 0% serum, which was significantly rescued by rapamycin. In 0% serum, absolute contraction by caffeine significantly decreased from Fresh, which was significantly rescued by rapamycin. In conclusion, expression of mTOR increased during serum-free organ culture of rat isolated mesenteric artery for 5 days, which may be at least partly responsible for the decreased smooth muscle contractility perhaps due to the decrease in the stored Ca2+ in smooth muscle.

Calmodulin-dependent Protein Kinase II/cAMP Response Element-binding Protein/Wnt/β-Catenin Signaling Cascade Regulates Angiotensin II-induced Podocyte Injury and Albuminuria

Angiotensin II (Ang II) plays a pivotal role in promoting podocyte dysfunction and albuminuria, however, the underlying mechanisms have not been fully delineated. In this study, we found that Ang II induced Wnt1 expression and β-catenin nuclear translocation in cultured mouse podocytes. Blocking Wnt signaling with Dickkopf-1 (Dkk1) or β-catenin siRNA attenuated Ang II-induced podocyte injury. Ang II could also induce the phosphorylation of calmodulin-dependent protein kinase (CaMK) II and cAMP response element-binding protein (CREB) in cultured podocytes. Blockade of this pathway with CK59 or CREB siRNA could significantly inhibit Ang II-induced Wnt/β-catenin signaling and podocyte injury. In in vivo studies, administration of Ang II promoted Wnt/β-catenin signaling, aggregated podocyte damage, and albuminuria in mice. CK59 could remarkably ameliorate Ang II-induced podocyte injury and albuminuria. Furthermore, ectopic expression of exogenous Dkk1 also attenuated Ang II-induced podocytopathy in mice. Taken together, this study demonstrates that the CaMK II/CREB/Wnt/β-catenin signaling cascade plays an important role in regulating Ang II-induced podocytopathy. Targeting this signaling pathway may offer renal protection against the development of proteinuric kidney diseases.

Blockade of sarcolemmal TRPV2 accumulation inhibits progression of dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a severe disorder defined by ventricular dilation and contractile dysfunction. Abnormal Ca(2+) handling is hypothesized to play a critical pathological role in DCM progression. The transient receptor potential vanilloid 2 (TRPV2) has been previously suggested as a candidate pathway for enhanced Ca(2+) entry. Here, we examined the sarcolemmal accumulation of TRPV2 in various heart-failure model animals and DCM patients, and assessed whether presently available inhibitory tools against TRPV2 ameliorate DCM symptoms. Immunological and cell physiological analyses revealed that TRPV2 is highly concentrated and activated in the ventricular sarcolemma of DCM patients and three animal models-δ-sarcoglycan-deficient hamsters (J2N-k), transgenic mice over-expressing sialytransferase (4C30), and doxorubicin (DOX)-induced DCM mice. Over-expression of the amino-terminal (NT) domain of TRPV2 could block the plasma membrane accumulation and influx of Ca(2+) via TRPV2. Transgenic (Tg) or adenoviral expression of the NT domain in DCM animals caused effective removal of sarcolemmal TRPV2 along with reduction in the phosphorylation of calmodulin-dependent protein kinase II (CaMKII) and reactive oxygen species (ROS) production, which were activated in DCM; further, it prevented ventricular dilation and fibrosis, ameliorated contractile dysfunction in DCM, and improved survival of the affected animals. The TRPV2 inhibitor tranilast markedly suppressed DCM progression. Sarcolemmal TRPV2 accumulation appears to have considerable pathological impact on DCM progression, and blockade of this channel may be a promising therapeutic strategy for treating advanced heart failure.

Serum containing Tongqiaohuoxue decoction suppresses glutamate-induced PC12 cell injury.

Glutamate application is an established method of inducing PC12 cell injury. PC12 cells were cultured with serum containing Tongqiaohuoxue decoction consisting of moschus, Carthamus tinctorius, Rhizoma chuanxiong, Semen pruni persicae, and Radix Paeoniae Rubra. After 24 hours of co-cultivation, glutamate (12.5 mM) was added to the culture medium. We found that serum containing Tongqiaohuoxue decoction prevented the increase in reactive oxygen species, and the decreases in superoxide dismutase and Na+-K+-ATPase activity, induced by glutamate. It also reduced the concentration of malondialdehyde, enhanced the mitochondrial transmembrane potential, inhibited the elevation of cellular calcium, and decreased phosphorylation of calmodulin-dependent protein kinase II. Thus, serum containing Tongqiaohuoxue decoction had protective effects on cell proliferation and membrane permeability in glutamate-injured PC12 cells.

Small mouse cholangiocytes proliferate in response to H1 histamine receptor stimulation by activation of the IP3/CaMK I/CREB pathway

Cholangiopathies are characterized by the heterogeneous proliferation of different-sized cholangiocytes. Large cholangiocytes proliferate by a cAMP-dependent mechanism. The function of small cholangiocytes may depend on the activation of inositol trisphosphate (IP(3))/Ca(2+)-dependent signaling pathways; however, data supporting this speculation are lacking. Four histamine receptors exist (HRH1, HRH2, HRH3, and HRH4). In several cells: 1) activation of HRH1 increases intracellular Ca(2+) concentration levels; and 2) increased [Ca(2+)](i) levels are coupled with calmodulin-dependent stimulation of calmodulin-dependent protein kinase (CaMK) and activation of cAMP-response element binding protein (CREB). HRH1 agonists modulate small cholangiocyte proliferation by activation of IP(3)/Ca(2+)-dependent CaMK/CREB. We evaluated HRH1 expression in cholangiocytes. Small and large cholangiocytes were stimulated with histamine trifluoromethyl toluidide (HTMT dimaleate; HRH1 agonist) for 24-48 h with/without terfenadine, BAPTA/AM, or W7 before measuring proliferation. Expression of CaMK I, II, and IV was evaluated in small and large cholangiocytes. We measured IP(3), Ca(2+) and cAMP levels, phosphorylation of CaMK I, and activation of CREB (in the absence/presence of W7) in small cholangiocytes treated with HTMT dimaleate. CaMK I knockdown was performed in small cholangiocytes stimulated with HTMT dimaleate before measurement of proliferation and CREB activity. Small and large cholangiocytes express HRH1, CaMK I, and CaMK II. Small (but not large) cholangiocytes proliferate in response to HTMT dimaleate and are blocked by terfenadine (HRH1 antagonist), BAPTA/AM, and W7. In small cholangiocytes, HTMT dimaleate increased IP(3)/Ca(2+) levels, CaMK I phosphorylation, and CREB activity. Gene knockdown of CaMK I ablated the effects of HTMT dimaleate on small cholangiocyte proliferation and CREB activation. The IP(3)/Ca(2+)/CaMK I/CREB pathway is important in the regulation of small cholangiocyte function.

Ca2+ and AMPK both mediate stimulation of glucose transport by muscle contractions.

It is now generally accepted that activation of AMP-activated protein kinase (AMPK) is involved in the stimulation of glucose transport by muscle contractions. However, earlier studies provided evidence that increases in cytosolic Ca(2+) mediate the effect of muscle contractions on glucose transport. The purpose of this study was to test the hypothesis that both the increase in cytosolic Ca(2+) and the activation of AMPK are involved in the stimulation of glucose transport by muscle contractions. Caffeine causes release of Ca(2+) from the sarcoplasmic reticulum. Incubation of rat epitrochlearis muscles with a concentration of caffeine that raises cytosolic Ca(2+) to levels too low to cause contraction resulted in an approximate threefold increase in glucose transport. Caffeine treatment also resulted in increased phosphorylation of calmodulin-dependent protein kinase (CAMK)-II in epitrochlearis muscle. The stimulation of glucose transport by caffeine was blocked by the Ca(2+)-CAMK inhibitors KN62 and KN93. Activation of AMPK with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) also resulted in an approximate threefold increase in glucose transport in the epitrochlearis. The increases in glucose transport induced by AICAR and caffeine were additive, and their combined effect was not significantly different from that induced by maximally effective contractile activity. KN62 and KN93 caused an approximately 50% inhibition of the stimulation of glucose transport by contractile activity. Our results provide evidence that both Ca(2+) and AMPK are involved in the stimulation of glucose transport by muscle contractions. They also suggest that the stimulation of glucose transport by Ca(2+) involves activation of CAMK.

Ca 2+-overload inhibits the cardiac SR Ca 2+–calmodulin protein kinase activity

There is increasing evidence to suggest that Ca 2+–calmodulin dependent protein kinase (CaMK) regulates the sarcoplasmic reticulum (SR) function and thus plays an important role in modulating the cardiac performance. Because intracellular Ca 2+-overload is an important factor underlying cardiac dysfunction in a heart disease, its effect on SR CaMK was examined in the isolated rat heart preparations. Ca 2+-depletion for 5 min followed by Ca 2+-repletion for 30 min, which is known to produce intracellular Ca 2+-overload, was observed to attenuate cardiac function as well as SR Ca 2+-uptake and Ca 2+-release activities. Attenuated SR function in the heart was associated with reduced CaMK phosphorylation of the SR Ca 2+-cycling proteins such as Ca 2+-release channel, Ca 2+-pump ATPase, and phospholamban, decreased CaMK activity, and depressed levels of SR Ca 2+-cycling proteins. These results indicate that alterations in cardiac performance and SR function following the occurrence of intracellular Ca 2+-overload may partly be due to changes in the SR CaMK activity.

Status of Ca2+/calmodulin protein kinase phosphorylation of cardiac SR proteins in ischemia-reperfusion.

Although the sarcoplasmic reticulum (SR) is known to regulate the intracellular concentration of Ca2+ and the SR function has been shown to become abnormal during ischemia-reperfusion in the heart, the mechanisms for this defect are not fully understood. Because phosphorylation of SR proteins plays a crucial role in the regulation of SR function, we investigated the status of endogenous Ca2+/calmodulin-dependent protein kinase (CaMK) and exogenous cAMP-dependent protein kinase (PKA) phosphorylation of the SR proteins in control, ischemic (I), and ischemia-reperfused (I/R) hearts treated or not treated with superoxide dismutase (SOD) plus catalase (CAT). SR and cytosolic fractions were isolated from control, I, and I/R hearts treated or not treated with SOD plus CAT, and the SR protein phosphorylation by CaMK and PKA, the CaMK- and PKA-stimulated Ca2+ uptake, and the CaMK, PKA, and phosphatase activities were studied. The SR CaMK and CaMK-stimulated Ca2+ uptake activities, as well as CaMK phosphorylation of Ca2+ pump ATPase (SERCA2a) and phospholamban (PLB), were significantly decreased in both I and I/R hearts. The PKA phosphorylation of PLB and PKA-stimulated Ca2+ uptake were reduced significantly in the I/R hearts only. Cytosolic CaMK and PKA activities were unaltered, whereas SR phosphatase activity in the I and I/R hearts was depressed. SOD plus CAT treatment prevented the observed alterations in SR CaMK and phosphatase activities, CaMK and PKA phosphorylations, and CaMK- and PKA-stimulated Ca2+ uptake. These results indicate that depressed CaMK phosphorylation and CaMK-stimulated Ca2+ uptake in I/R hearts may be due to a depression in the SR CaMK activity. Furthermore, prevention of the I/R-induced alterations in SR protein phosphorylation by SOD plus CAT treatment is consistent with the role of oxidative stress during ischemia-reperfusion injury in the heart.

Determination and analysis of the primary structure of the nerve terminal specific phosphoprotein, synapsin I.

A rat brain cDNA clone containing an open reading frame encoding the neuron-specific protein synapsin I has been sequenced. The sequence predicts a protein of 691 amino acids with a mol. wt of 73 kd. This is in excellent agreement with the size of rat brain synapsin Ib measured by SDS--polyacrylamide gel electrophoresis. Inspection of the predicted primary structure has revealed the probable sites for synapsin I phosphorylation by the cAMP-dependent and Ca2+/calmodulin-dependent protein kinases. All of the biochemically observed intermediates of synapsin I digestion by collagenase can be verified by inspection of the sequence, and the collagenase-resistant fragment has been defined as the amino-terminal 439 amino acids of the molecule. Predictions of sequence secondary structure and hydrophobicity suggest that a central domain of approximately 270 amino acids may exist as a folded, globular core. The carboxyl-terminal domain of the protein (the region sensitive to collagenase digestion) contains sites for Ca2+/calmodulin-dependent protein kinase phosphorylation. These sites are flanked by three regions of repeating amino acid sequence that are proposed to be the synaptic vesicle-binding domain of synapsin I. This region also shares homology with the actin-binding proteins profilin and villin. The characteristics of the synapsin I sequence do not support extensive homology with the erythrocyte cytoskeletal protein 4.1.