Effect of Nanomolar Concentrations of Sodium Dodecyl Sulfate, a Catalytic Inductor of α-Helices, on Human Calcitonin Incorporation and Channel Formation in Planar Lipid Membranes

Abstract

Human Calcitonin (hCt) is a peptide hormone which has a regulatory action in calcium-phosphorus metabolism. It is currently used as a therapeutic tool in bone pathologies such as osteoporosis and Paget's disease. However, due to its amphiphilic property tends to form a gelatinous solution in water which consists of fibrils that limits its therapeutic use. Here we show that sodium dodecyl sulfate (SDS), an anionic detergent able to induce and stabilize alpha-helices in polypeptides, at a monomeric concentration ranging between 0.26 mM-5 pM (all concentrations are below the CMC), increases the rate and number of hCt channel formation in planar lipid membranes, at both high and low hCt concentrations, with a maximum increase at a molecular hCt/SDS ratio of 1000:1. This effect could be interpreted as a counteraction to the fibrillation process of hCt molecules by removing molecules available for aggregation from the fluid; furthermore, this action, independently of channel formation in the cell membrane, could improve the peptide-receptor interaction. The action of SDS could be attributable to the strength of the sulfate negative charge and the hydrophobic chain; in fact, a similar effect was obtained with lauryl sarcosine and not with a neutral detergent such as n-dodecyl-beta-D-maltoside. The very low molecular ratio between SDS and peptide is suggestive of a possible catalytic action of SDS that could induce alpha-helices, the appropriate structures for interacting with the membrane. Moreover, in the experimental conditions investigated, the addition of SDS does not modify the membrane's electrical properties and most of the channel properties. This finding may contribute to the knowledge of environment-folding diseases due to protein and peptides.

How “Full” is “Full Fusion” during Exocytosis from Dense Core Vesicles? Effect of SDS on “Quantal” Release and Final Fusion Pore Size

“…The responses observed during successive stimulations up to the 7 th one resulted quantitatively undistinguishable from those evoked by the first one (data not shown) as evidenced qualitatively in Figure 2D showing that no significant long-term effects occurred. In agreement with previous reports, [49][50][51][52][53] this survey of SDS on exocytosis confirmed that 250-350 μM corresponded to an adequate concentration range for our purpose in this study. Yet, to ensure the absence of any non-obvious long-term effects, only the spikes delivered during the first 10 s range after the first stimulation were treated quantitatively.…”

“…On the other hand, SDS is reported to stabilize the transient nanopores that constantly form in cellular membranes 38 or contribute to the formation of trans-membrane channels. 49,50 Hence, Ca 2+ intake is expected to occur spontaneously after brief SDS stimulation, thus initiating exocytosis by triggering the physiological Ca 2+ -induced cascade recalled above. 9 Therefore, to validate the physiological relevance of the results presented and discussed hereafter it was essential to firstly assess if this is effectively the case when exocytosis is elicited by SDS.…”

“…Presumably, at this concentration, the cell membrane structure is so drastically affected so that significant SDS quantities may diffuse inside the cell to reach vesicles and lyse them allowing a considerable quantity of catecholamine cations to be released and freely diffuse toward the electrode. 49,50 This would lead to broad diffusion-controlled current traces while some intact vesicles may still provide sharp spikes. However, this does not evidence that such spikes featured normal exocytotic processes.…”

“…32 In this work, we wish to contribute to this search by examining the quantitative and kinetic changes induced in PC12 exocytotic events when these are elicited following their brief stimulations by very dilute sodium dodecyl sulfate (SDS) solutions. Based on previous studies, SDS concentrations lower than 400 μM cannot affect cells membranes structure 49,50 but may be transferred across them and weaken actin assembling in sub-membrane cytoskeletons. 49 It is shown hereafter that eliciting release with SDS 350 μM led to physiologically realistic vesicular exocytotic events, i.e., comparable to those elicited by classical methods such as brief stimulations by K + 105 mM, except that the released quantities resulted almost doubled.…”

Conformation and Lipid Binding of a C-Terminal (198−243) Peptide of Human Apolipoprotein A-I

“…BOG, DPC and DHPC). In addition, SDS was reported to induce α-helical structure formation in the peptide of a membrane protein at SDS:peptide 1:1000 molar [44] and was proposed to be a "catalytic inducer" of α-helices. The mechanism of how SDS folds apolipoproteins into helix requires further investigation.…”