In vitro work on synucein, tau, amyloid beta and most other amyloid proteins can usually Biosafety Level 1 in the US unless other factors are involved, which I believe corresponds to ML1 in the Netherlands. The regulations on transgenic mice are considerably more complicated.
The requirements for prion proteins are much higher, BSL 3 for human prions and usually BSL 2 for animal derived prions.
ML1 would be sufficient. If you are working with heterologous expression of alpha-synuclein in bacteria or cells lines or even with animal expression using viruses, you would probably have to look into upgrading to a more appropriate biosafety level.