AF488 C5 Maleimide

Guide (The following is our recommended protocol. This protocol is for guidance only and should be modified according to your specific needs).

1. Stock Solution Preparation
1.1 Solvent: 10 mM sodium phosphate buffer pH 7.4; alternative: anhydrous DMSO.
1.2 Concentration recommendation: 4x molar excess relative to tau K18 protein; alternative: 5 mg/mL.

2. Working Solution Preparation
2.1 Diluent: Cell culture medium (1:1 minimal essential medium/F12 Ham medium for SH-SY5Y cells; Axol Neural Maintenance medium for hiPSC-derived neurons); alternative: buffer lacking free thiols (PBS or Instant Ocean buffer).
2.2 Working concentration: 5 μM; alternative: 25 µg/mL.
2.3 Note: Adjust working solution concentration as needed; prepare fresh before use.

3. Staining Procedure
3.1 Sample type descriptions
3.1.1 For adherent mammalian cells[1]: SH-SY5Y human neuroblastoma cells; human induced pluripotent stem cell-derived cortical neurons; no trypsinization mentioned for this staining step.
3.1.2 For suspension bacterial cells[2]: C. crescentus, V. cholerae; centrifuge at species-appropriate speed (5,000g for C. crescentus; 16,000g for V. cholerae) for 1 min at room temperature before resuspension.
3.2 Incubation conditions
3.2.1 For adherent mammalian cells[1]: Incubate samples with 5 μM AF488 C5 Maleimide-labeled tau K18 oligomers at 37°C, 5% CO₂ for 24 h.
3.2.2 For suspension bacterial cells[2]: Incubate with 25 µg/mL AF488 C5 Maleimide at room temperature for 5-30 min.
3.3 Washing steps
3.3.1 For SH-SY5Y cells[1]: Wash with warm phosphate buffered saline once after incubation.
3.3.2 For hiPSC-derived neurons[1]: Wash with Dulbecco’s PBS twice after incubation.
3.3.3 For suspension bacterial cells[2]: Centrifuge cells at species-appropriate speed for 1 min, discard supernatant, resuspend in 100 µl fresh buffer/medium, and centrifuge again for 1 min.

4. Controls
4.1 Unlabeled tau K18 oligomer control: Prepared identically except equal volume of 10 mM sodium phosphate buffer pH 7.4 is used in place of AF488 C5 Maleimide.
4.2 Negative control using non-cysteine knock-in parent strain to exclude non-specific labeling interference.

5. Detection & Analysis
5.1 Instrument type: Confocal microscope; epifluorescence microscope with FITC filter set.
5.2 Ex/Em wavelengths: Consistent with Alexa Fluor 488 properties.
5.3 Result analysis
5.3.1 For adherent mammalian cells[1]: Green fluorescence from AF488 C5 Maleimide; for SH-SY5Y cells, labeled tau K18 oligomers show diffused cytoplasmic distribution or localized punctate staining in intracellular spaces; for hiPSC-derived neurons, labeled tau K18 oligomers accumulate in cell soma and neurites, with evidence of endocytic internalization.
5.3.2 For suspension bacterial cells[2]: Bright green fluorescence is expected on surface-exposed bacterial pili, with peripheral cell body fluorescence from labeled pilins in the cytoplasmic membrane; unperturbed labeled pili exhibit dynamic extension and retraction over time-lapse imaging, while obstructed pili remain static; labeling efficiency varies by cysteine substitution position, with some positions showing bright labeling, weak labeling, or no labeling.

MedChemExpress (MCE) has not independently confirmed the accuracy of these methods. They are for reference only.